Encoder, decoder, encoding method, and decoding method

ABSTRACT

An encoder includes circuitry and memory. Using the memory, the circuitry performs prediction on an image. A motion vector predictor list used in the prediction includes a spatially neighboring motion vector predictor obtained from a block spatially neighboring a current block, and a spatially broad motion vector predictor obtained from a block positioned at any of a plurality of predetermined positions in a second range that is broader than a first range that spatially neighbors the current block. The plurality of predetermined positions are defined by a regular interval using the top-left of a current picture as a reference point.

FIELD

The present disclosure relates to, for example, an encoder that encodesa video including a plurality of pictures.

BACKGROUND

One example of a conventional video encoding standard is H.265, alsoreferred to as high efficiency video coding (HEVC) (Non PatentLiterature (NPL) 1).

CITATION LIST Non Patent Literature

-   [NPL 1] H.265 (ISO/IEC 23008-2 HEVC)/HEVC (High Efficiency Video    Coding)

SUMMARY Technical Problem

However, prediction precision can be improved upon. Moreover, whenprediction precision is improved, the amount of information to be storedin, for example, memory, increases, and the scale of the circuitryincreases.

In view of this, the present disclosure provides an encoder, etc., thatfurther improves prediction precision, and can reduce the accompanyingincrease in information to be stored in, for example, memory, andincrease in circuitry scale.

Solution to Problem

An encoder according to one aspect of the present disclosure encodes avideo and includes circuitry and memory. Using the memory, the circuitrygenerates a motion vector predictor list by registering motion vectorpredictors obtained by referencing a plurality of encoded blocks,selects one motion vector predictor from the motion vector predictorlist, and implements a prediction mode that performs motion compensationusing a motion vector derived from the one motion vector predictor. Themotion vector predictor list includes a spatially neighboring motionvector predictor obtained from a block spatially neighboring a currentblock, and a spatially broad motion vector predictor obtained from ablock positioned at any of a plurality of predetermined positions in asecond range that is broader than a first range that spatially neighborsthe current block. Information on motion vectors to be referenced in theprediction mode is managed in association with reference blocks of aspecific size. The plurality of predetermined positions are positionsof, from among the reference blocks, reference blocks in positionsdefined by a regular interval using a current picture as a reference.

Note that these general and specific aspects may be implemented using asystem, a device, a method, an integrated circuit, a computer program,or a non-transitory computer-readable recording medium such as a CD-ROM,or any combination thereof.

Advantageous Effects

The encoder, etc., according to one aspect of the present disclosurefurther improves prediction precision, and can reduce the accompanyingincrease in information to be stored in, for example, memory, andincrease in circuitry scale.

BRIEF DESCRIPTION OF DRAWINGS

These and other objects, advantages and features of the disclosure willbecome apparent from the following description thereof taken inconjunction with the accompanying drawings that illustrate a specificembodiment of the present disclosure.

FIG. 1 is a block diagram illustrating a functional configuration of theencoder according to Embodiment 1.

FIG. 2 illustrates one example of block splitting according toEmbodiment 1.

FIG. 3 is a chart indicating transform basis functions for eachtransform type.

FIG. 4A illustrates one example of a filter shape used in ALF.

FIG. 4B illustrates another example of a filter shape used in ALF.

FIG. 4C illustrates another example of a filter shape used in ALF.

FIG. 5A illustrates 67 intra prediction modes used in intra prediction.

FIG. 5B is a flow chart for illustrating an outline of a predictionimage correction process performed via OBMC processing.

FIG. 5C is a conceptual diagram for illustrating an outline of aprediction image correction process performed via OBMC processing.

FIG. 5D illustrates one example of FRUC.

FIG. 6 is for illustrating pattern matching (bilateral matching) betweentwo blocks along a motion trajectory.

FIG. 7 is for illustrating pattern matching (template matching) betweena template in the current picture and a block in a reference picture.

FIG. 8 is for illustrating a model assuming uniform linear motion.

FIG. 9A is for illustrating deriving a motion vector of each sub-blockbased on motion vectors of neighboring blocks.

FIG. 9B is for illustrating an outline of a process for deriving amotion vector via merge mode.

FIG. 9C is a conceptual diagram for illustrating an outline of DMVRprocessing.

FIG. 9D is for illustrating an outline of a prediction image generationmethod using a luminance correction process performed via LICprocessing.

FIG. 10 is a block diagram illustrating a functional configuration ofthe decoder according to Embodiment 1.

FIG. 11 illustrates a generation method of a motion vector predictorlist in merge mode that uses spatially broad motion vector predictorsaccording to Embodiment 1.

FIG. 12 is a flow chart showing processes performed in merge mode thatuses spatially broad motion vector predictors according to Embodiment 1.

FIG. 13 illustrates a first method of referencing spatially broadvectors in merge mode that uses spatially broad motion vector predictorsaccording to Embodiment 1.

FIG. 14 illustrates a second method of referencing spatially broadvectors in merge mode that uses spatially broad motion vector predictorsaccording to Embodiment 1.

FIG. 15 illustrates a third method of referencing spatially broadvectors in merge mode that uses spatially broad motion vector predictorsaccording to Embodiment 1.

FIG. 16 is a flow chart showing a management method for memory, etc.,that stores motion vectors for referencing spatially broad motion vectorpredictors according to an embodiment.

FIG. 17 is a block diagram illustrating an implementation example of anencoder according to Embodiment 1.

FIG. 18 is a flow chart illustrating an example of operations performedby an encoder according to Embodiment 1.

FIG. 19 is a block diagram illustrating an implementation example of adecoder according to Embodiment 1.

FIG. 20 is a flow chart illustrating an example of operations performedby a decoder according to Embodiment 1.

FIG. 21 illustrates an overall configuration of a content providingsystem for implementing a content distribution service.

FIG. 22 illustrates one example of encoding structure in scalableencoding.

FIG. 23 illustrates one example of encoding structure in scalableencoding.

FIG. 24 illustrates an example of a display screen of a web page.

FIG. 25 illustrates an example of a display screen of a web page.

FIG. 26 illustrates one example of a smartphone.

FIG. 27 is a block diagram illustrating a configuration example of asmartphone.

DESCRIPTION OF EMBODIMENTS

(Underlying Knowledge Forming Basis of the Present Disclosure)

For example, in H.265, various prediction modes can be used in theencoding, etc., of a video. In a prediction mode, for example, encoder100 or decoder 200 performs prediction by selecting an appropriatemotion vector from motion vector candidates derived from motion vectorinformation on processed blocks that neighbor the current block, andperforming motion compensation.

For example, restricting blocks to be referenced for deriving the motionvector candidates to only encoded blocks that neighbor the current blockprevents appropriate selection of motion vectors and merely improvescoding efficiency by a certain amount. Moreover, assume encoder 100 ordecoder 200 also refer to other blocks in addition to the encoded blocksthat neighbor the current block, in order to select more appropriatemotion vectors compared to those selected with conventional techniques.In such a case, the amount of information that encoder 100 or decoder200 is to store in, for example, memory, increases, and the scale of thecircuitry included in encoder 100 or decoder 200 increases.

For example, an encoder according to one aspect of the presentdisclosure encodes a video and includes circuitry and memory. Using thememory, the circuitry generates a motion vector predictor list byregistering motion vector predictors obtained by referencing a pluralityof encoded blocks, selects one motion vector predictor from the motionvector predictor list, and implements a prediction mode that performsmotion compensation using a motion vector derived from the one motionvector predictor. The motion vector predictor list includes a spatiallyneighboring motion vector predictor obtained from a block spatiallyneighboring a current block, and a spatially broad motion vectorpredictor obtained from a block positioned at any of a plurality ofpredetermined positions in a second range that is broader than a firstrange that spatially neighbors the current block. Information on motionvectors to be referenced in the prediction mode is managed inassociation with reference blocks of a specific size. The plurality ofpredetermined positions are positions of, from among the referenceblocks, reference blocks in positions defined by a regular intervalusing a current picture as a reference.

This enables the encoder to obtain motion vectors by referencing blocksin a range that is broader than the conventional range. Accordingly, theencoder can improve coding efficiency since more appropriate motionvectors can be selected than those selected with conventionaltechniques. Moreover, since the blocks to be referenced are blockspositioned at a regular interval, the number of blocks to be referencedcan be reduced. Accordingly, the encoder allows for a reduction in thescale of the circuitry included in the encoder since the amount ofinformation to be stored in, for example, memory, can be reduced.Moreover, the encoder can make the blocks to be referenced to be blockshaving the same size. Moreover, the encoder can manage motion vectors ona block-by-block basis of blocks having the same size.

Moreover, for example, in the encoder according to one aspect of thepresent disclosure, the prediction mode is a merge mode.

This enables the encoder to, upon prediction, select appropriate motionvectors from among motion vector candidates derived from motioninformation on encoded blocks, and encode only those indices thatindicate motion vector information. This in turn enables the encoder toinhibit the motion vector encoding amount.

Moreover, for example, in the encoder according to one aspect of thepresent disclosure, blocks positioned at the plurality of predeterminedpositions are defined as reference blocks of a specific size, andinformation on motion vectors to be referenced in the prediction mode ismanaged in association with the reference blocks.

This enables the encoder to make the blocks to be referenced to beblocks having the same size. Moreover, the encoder can manage motionvectors on a block-by-block basis of blocks having the same size.

Moreover, for example, in the encoder according to one aspect of thepresent disclosure, the reference block has a size of 4×4 pixels.

This enables the encoder to reference blocks for obtaining motionvectors in units of 4×4 pixel blocks.

Moreover, for example, in the encoder according to one aspect of thepresent disclosure, the regular interval is an interval of 16 pixels ina horizontal direction and 16 pixels in a vertical direction.

This enables the encoder to reference blocks for obtaining motionvectors spaced 16 pixels apart.

Moreover, for example, in the encoder according to one aspect of thepresent disclosure, the block positioned at any of the plurality ofpredetermined positions is, from among a plurality of reference blockseach defined as the reference block, a block that is positioned outsideof the current block and is one of a predetermined number of sequentialreference blocks in any one of down, left-down, left, left-up, up,right-up, and right directions, from at least one of reference blocksthat are closest to the current block from among reference blocks thatare in positions defined by the regular interval and cover top and leftsides of the current block.

This enables the encoder to obtain more motion vectors than withconventional techniques, by referencing blocks in positions thatsurround the current block and blocks in the surrounding area thereof.Accordingly, in prediction mode, the encoder can select more appropriatemotion vectors than those selected with conventional techniques.

Moreover, for example, in the encoder according to one aspect of thepresent disclosure, the surrounding blocks in the spatially broad areamay be processed blocks in sequences of blocks selected such that,regardless of the size of the current block, the number of sequences ofsequential blocks in the left and up directions, regarding the left andtop edges on the outside of and closest to the current block, is aspecific number or less.

This enables the encoder to restrict the number of blocks to bereferenced for obtaining motion vectors. Accordingly, the encoder allowsfor the amount of information to be stored in, for example, memory, tobe reduced, and allows for a reduction in the scale of the circuitryincluded in the encoder.

Moreover, for example, in the encoder according to one aspect of thepresent disclosure, the circuitry: scans, in a specific order ofproximity to the current block, blocks positioned at any one of theplurality of predetermined positions in a range that is broader than arange that spatially neighbors the current block; and registers themotion vector predictors obtained from the blocks positioned at any oneof the plurality of predetermined positions in the range that is broaderthan the range that spatially neighbors the current block into themotion vector predictor list as the spatially broad motion vectorpredictors, until a total number of the motion vector predictorsregistered reaches a first number.

This enables the encoder to obtain motion vectors by referencing blocksin the surrounding area of the current block, in order of proximity tothe current block. Moreover, the encoder can register a predeterminednumber of the obtained motion vectors as a list. This enables theencoder to hold, as a list, motion vectors obtained by referencingblocks in a range that is broader than the conventional range.

Moreover, for example, in the encoder according to one aspect of thepresent disclosure, the circuitry is capable of adaptively changing theregular interval or the second range based on a capability of theencoder or a size of the current picture.

This enables the encoder to reference an appropriate number of blocks inprediction mode, based on the capability of the encoder or the size ofthe current picture. Accordingly, the encoder can store, in memory,etc., an appropriate amount of information based on the capability ofthe encoder or the size of the current picture.

Moreover, for example, in the encoder according to one aspect of thepresent disclosure, the circuitry writes, into the slice, picture, orsequence header, information specifying the regular interval or thesecond range.

This enables the encoder to specify the number of blocks, for example,to be referenced in prediction mode, on a per-slice, per-picture, orper-sequence basis.

Moreover, for example, in the encoder according to one aspect of thepresent disclosure, when the capability of the encoder is a firstcapability that is lower than a first reference, the regular interval isa first interval, and when the capability of the encoder is a secondcapability that is higher than the first reference, the regular intervalis a second interval that is narrower than the first interval.

With this, when the capability of the encoder is lower than a referencecapability, the encoder can restrict the number of blocks to bereferenced by increasing the interval between positions of blocks to bereferenced. Moreover, with this, when the capability of the encoder ishigher than a reference capability, the encoder can increase the numberof blocks to be referenced to more than when the capability of theencoder is lower than a reference capability, by reducing the intervalbetween positions of blocks to be referenced. Accordingly, the encodercan appropriately set the number of blocks to be referenced inaccordance with the capability of the encoder.

Moreover, for example, in the encoder according to one aspect of thepresent disclosure, when the capability of the encoder is a thirdcapability that is lower than a second reference, the number ofreference blocks in predetermined positions in the second range to bereferenced for motion vector predictor list generation is a firstnumber, and when the capability of the encoder is a fourth capabilitythat is higher than the second reference, the number of reference blocksin predetermined positions in the second range to be referenced formotion vector predictor list generation is a second number that isgreater than the first number.

With this, when the capability of the encoder is lower than a referencecapability, the encoder can restrict the number of blocks to bereferenced by reducing the range of positions of blocks to bereferenced. Moreover, with this, when the capability of the encoder ishigher than a reference capability, the encoder can increase the numberof blocks to be referenced to more than when the capability of theencoder is lower than a reference capability, by increasing the range ofpositions of blocks to be referenced. Accordingly, the encoder canappropriately set the number of blocks to be referenced in accordancewith the capability of the encoder.

Moreover, for example, in the encoder according to one aspect of thepresent disclosure, when the size of the current picture is a first sizethat is larger than a third reference, the regular interval is a thirdinterval, and when the size of the current picture is a second size thatis smaller than the third reference, the regular interval is a fourthinterval that is narrower than the third interval.

With this, when the size of the current picture is larger than areference size, by increasing the interval between blocks to bereferenced, the encoder can prevent the number of blocks to bereferenced from excessively increasing, more so than when the size ofthe current picture is smaller than a reference size. In other words,the encoder can reduce the number of blocks to be referenced when thesize of the current picture is larger than a reference size. Moreover,with this, when the size of the current picture is smaller than areference size, by reducing the interval between blocks to bereferenced, the encoder can secure a sufficient number of blocks to bereferenced, more so than when the size of the current picture is largerthan a reference size. In other words, when the size of the currentpicture is smaller than a reference size, the encoder can prevent thenumber of blocks to be referenced from being insufficient and thusprevent the inability to use a sufficient amount of motion vectors inprediction mode. Accordingly, the encoder can appropriately set thenumber of blocks to be referenced in accordance with the size of thecurrent picture.

Moreover, for example, in the encoder according to one aspect of thepresent disclosure, when the size of the current picture is a third sizethat is larger than a fourth reference, the number of reference blocksin predetermined positions in the second range to be referenced formotion vector predictor list generation is a third number, and when thesize of the current picture is a fourth size that is smaller than thefourth reference, the number of reference blocks in predeterminedpositions in the second range to be referenced for motion vectorpredictor list generation is a fourth number that is less than the thirdnumber.

With this, when the size of the current picture is larger than areference size, the encoder can increase the number of blocks to bereferenced, more so than when the size of the current picture is smallerthan a reference size. Moreover, with this, when the size of the currentpicture is smaller than a reference size, the encoder can restrictnumber of blocks to be referenced, more so than when the size of thecurrent picture is larger than a reference size. Accordingly, theencoder can appropriately set the number of blocks to be referenced inaccordance with the size of the current picture.

Moreover, for example, in the encoder according to one aspect of thepresent disclosure, the circuitry stores information on motion vectorsassigned to reference blocks in the memory.

This enables the encoder to store, in memory, etc., information onmotion vectors on a block-by-block basis of blocks that have the same,specific size.

Moreover, for example, in the encoder according to one aspect of thepresent disclosure, the circuitry stores information on motion vectorsin units of reference blocks in the memory, and when the current blockis a block including one of the reference blocks in a position definedby the regular interval, stores information on a motion vector derivedfrom the current block in the memory.

This enables the encoder to store, in memory, etc., information onmotion vectors obtained from blocks in positions that surround thecurrent block and blocks in the surrounding area thereof. Moreover, thisenables the encoder to store, in memory, etc., information on motionvectors on a block-by-block basis of blocks that have the same, specificsize.

Moreover, for example, in the encoder according to one aspect of thepresent disclosure, when the current block is a last block in a currentCTU, the circuitry enables deletion of, from among information on themotion vectors stored in the memory, information on a motion vector in aregion that will not be used in referencing performed in subsequent CTUprocessing.

This enables the encoder to reduce the amount of information to bestored in, for example, memory, by enabling deletion of information thatwill not be referenced in subsequent CTU processing.

For example, a decoder according to one aspect of the present disclosuredecodes a video and includes circuitry and memory. Using the memory, thecircuitry generates a motion vector predictor list by registering motionvector predictors obtained by referencing a plurality of decoded blocks,selects one motion vector predictor from the motion vector predictorlist, and implements a prediction mode that performs motion compensationusing a motion vector derived from the one motion vector predictor. Themotion vector predictor list includes a spatially neighboring motionvector predictor obtained from a block spatially neighboring a currentblock, and a spatially broad motion vector predictor obtained from ablock positioned at any of a plurality of predetermined positions in asecond range that is broader than a first range that spatially neighborsthe current block. Information on motion vectors to be referenced in theprediction mode is managed in association with reference blocks of aspecific size. The plurality of predetermined positions are positionsof, from among the reference blocks, reference blocks in positionsdefined by a regular interval using a top-left of a current picture as areference point.

This enables the decoder to obtain motion vectors by referencing blocksin a range that is broader than the conventional range. Accordingly, thedecoder can improve decoding efficiency since more appropriate motionvectors can be selected than those selected with conventionaltechniques. Moreover, since the blocks to be referenced are blockspositioned at a regular interval, the number of blocks to be referencedcan be reduced. Accordingly, the decoder allows for a reduction in thescale of the circuitry included in the decoder since the amount ofinformation to be stored in, for example, memory, can be reduced.Moreover, the decoder can make the blocks to be referenced to be blockshaving the same size. Moreover, the decoder can manage motion vectors ona block-by-block basis of blocks having the same size.

Moreover, for example, in the decoder according to one aspect of thepresent disclosure, the prediction mode is a merge mode.

This enables the decoder to, upon prediction, perform motioncompensation using motion vectors obtained by decoding the indicesindicating motion vector information. This in turn enables the decoderto inhibit the coding amount.

Moreover, for example, in the decoder according to one aspect of thepresent disclosure, blocks positioned at the plurality of predeterminedpositions are defined as reference blocks of a specific size, andinformation on motion vectors to be referenced in the prediction mode ismanaged in association with the reference blocks.

With this, the decoder can make the blocks to be referenced to be blockshaving the same size. Moreover, the decoder can manage motion vectors ona block-by-block basis of blocks having the same size.

Moreover, for example, in the decoder according to one aspect of thepresent disclosure, the reference block has a size of 4×4 pixels.

This enables the decoder to reference blocks for obtaining motionvectors in units of 4×4 pixel blocks.

Moreover, for example, in the decoder according to one aspect of thepresent disclosure, the regular interval is an interval of 16 pixels ina horizontal direction and 16 pixels in a vertical direction.

This enables the decoder to reference blocks for obtaining motionvectors spaced 16 pixels apart.

Moreover, for example, in the decoder according to one aspect of thepresent disclosure, the block positioned at any of the plurality ofpredetermined positions is, from among a plurality of reference blockseach defined as the reference block, a block that is positioned outsideof the current block and is one of a predetermined number of sequentialreference blocks in any one of down, left-down, left, left-up, up,right-up, and right directions, from at least one of reference blocksthat are closest to the current block from among reference blocks thatare in positions defined by the regular interval and cover top and leftsides of the current block.

This enables the decoder to obtain more motion vectors than withconventional techniques, by referencing blocks in positions thatsurround the current block and blocks in the surrounding area thereof.Accordingly, in prediction mode, the decoder can select more appropriatemotion vectors than those selected with conventional techniques.

Moreover, for example, in the decoder according to one aspect of thepresent disclosure, a block positioned in the predetermined position ofthe current block is a decoded block in sequences of blocks selectedsuch that the number of sequences of sequential blocks in the left andup directions, regarding the left and top edges on the outside of andclosest to the current block, is a predetermined number or less.

This enables the decoder to restrict the number of blocks to bereferenced for obtaining motion vectors. Accordingly, the decoder allowsfor a reduction in the scale of the circuitry included in the decodersince the amount of information to be stored in, for example, memory,can be reduced.

Moreover, for example, in the decoder according to one aspect of thepresent disclosure, the circuitry: scans, in a specific order ofproximity to the current block, blocks positioned at any one of theplurality of predetermined positions in a range that is broader than arange that spatially neighbors the current block; and registers themotion vector predictors obtained from the blocks positioned at any oneof the plurality of predetermined positions in the range that is broaderthan the range that spatially neighbors the current block into themotion vector predictor list as the spatially broad motion vectorpredictors, until a total number of the motion vector predictorsregistered reaches a first number.

This enables the decoder to obtain motion vectors by referencing blocksin the surrounding area of the current block, in order of proximity tothe current block. Moreover, the decoder can register a predeterminednumber of the obtained motion vectors as a list. This enables thedecoder to hold, as a list, motion vectors obtained by referencingblocks in a range that is broader than the conventional range.

Moreover, for example, in the decoder according to one aspect of thepresent disclosure, the circuitry is capable of adaptively changing theregular interval or the second range based on a capability of thedecoder or a size of the current picture.

This enables the decoder to reference an appropriate number of blocks inprediction mode, based on the capability of the decoder or the size ofthe current picture. Accordingly, the decoder can store, in memory,etc., an appropriate amount of information based on the capability ofthe decoder or the size of the current picture.

Moreover, for example, the decoder according to one aspect of thepresent disclosure writes, into the slice, picture, or sequence header,information specifying the regular interval or the second range.

This enables the decoder to specify the number of blocks, for example,to be referenced in prediction mode, on a per-slice, per-picture, orper-sequence basis.

Moreover, for example, in the decoder according to one aspect of thepresent disclosure, when the capability of the decoder is a firstcapability that is lower than a first reference, the regular interval isa first interval, and when the capability of the decoder is a secondcapability that is higher than the first reference, the regular intervalis a second interval that is narrower than the first interval.

With this, when the capability of the decoder is lower than a referencecapability, the decoder can restrict the number of blocks to bereferenced by increasing the interval between positions of blocks to bereferenced. Moreover, with this, when the capability of the decoder ishigher than a reference capability, the decoder can increase the numberof blocks to be referenced to more than when the capability of thedecoder is lower than a reference capability, by reducing the intervalbetween positions of blocks to be referenced. Accordingly, the decodercan appropriately set the number of blocks to be referenced inaccordance with the capability of the decoder.

Moreover, for example, in the decoder according to one aspect of thepresent disclosure, when the capability of the decoder is a thirdcapability that is lower than a second reference, the number ofreference blocks in predetermined positions in the second range to bereferenced for motion vector predictor list generation is a firstnumber, and when the capability of the decoder is a fourth capabilitythat is higher than the second reference, the number of reference blocksin predetermined positions in the second range to be referenced formotion vector predictor list generation is a second number that isgreater than the first number.

With this, when the capability of the decoder is lower than a referencecapability, the decoder can restrict the number of blocks to bereferenced by reducing the range of positions of blocks to bereferenced. Moreover, with this, when the capability of the decoder ishigher than a reference capability, the decoder can increase the numberof blocks to be referenced to more than when the capability of thedecoder is lower than a reference capability, by increasing the range ofpositions of blocks to be referenced. Accordingly, the decoder canappropriately set the number of blocks to be referenced in accordancewith the capability of the decoder.

Moreover, for example, in the decoder according to one aspect of thepresent disclosure, when the size of the current picture is a first sizethat is larger than a third reference, the regular interval is a thirdinterval, and when the size of the current picture is a second size thatis smaller than the third reference, the regular interval is a fourthinterval that is narrower than the third interval.

With this, when the size of the current picture is larger than areference size, by increasing the interval between blocks to bereferenced, the decoder can prevent the number of blocks to bereferenced from excessively increasing, more so than when the size ofthe current picture is smaller than a reference size. In other words,the decoder can reduce the number of blocks to be referenced when thesize of the current picture is larger than a reference size. Moreover,with this, when the size of the current picture is smaller than areference size, by reducing the interval between blocks to bereferenced, the decoder can secure a sufficient number of blocks to bereferenced, more so than when the size of the current picture is largerthan a reference size. In other words, when the size of the currentpicture is smaller than a reference size, the decoder can prevent thenumber of blocks to be referenced from being insufficient and thusprevent the inability to use a sufficient amount of motion vectors inprediction mode. Accordingly, the decoder can appropriately set thenumber of blocks to be referenced in accordance with the size of thecurrent picture.

Moreover, for example, in the decoder according to one aspect of thepresent disclosure, when the size of the current picture is a third sizethat is larger than a fourth reference, the number of reference blocksin predetermined positions in the second range to be referenced formotion vector predictor list generation is a third number, and when thesize of the current picture is a fourth size that is smaller than thefourth reference, the number of reference blocks in predeterminedpositions in the second range to be referenced for motion vectorpredictor list generation is a fourth number that is less than the thirdnumber.

With this, when the size of the current picture is larger than areference size, the decoder can increase the number of blocks to bereferenced, more so than when the size of the current picture is smallerthan a reference size. Moreover, with this, when the size of the currentpicture is smaller than a reference size, the decoder can restrictnumber of blocks to be referenced, more so than when the size of thecurrent picture is larger than a reference size. Accordingly, thedecoder can appropriately set the number of blocks to be referenced inaccordance with the size of the current picture.

Moreover, for example, in the decoder according to one aspect of thepresent disclosure, the circuitry stores information on motion vectorsassigned to reference blocks in the memory.

This enables the decoder to store, in memory, etc., information onmotion vectors on a block-by-block basis of blocks that have the same,specific size.

Moreover, for example, in the decoder according to one aspect of thepresent disclosure, the circuitry stores information on motion vectorsassigned to the reference blocks in the memory, and when the currentblock is a block including one of the reference blocks in a positiondefined by the regular interval, stores information on a motion vectorderived from the current block in the memory.

This enables the decoder to store, in memory, etc., information onmotion vectors obtained from blocks in positions that surround thecurrent block and blocks in the surrounding area thereof. Moreover, thedecoder can store, in memory, etc., information on motion vectors on ablock-by-block basis of blocks that have the same, specific size.

Moreover, for example, in the decoder according to one aspect of thepresent disclosure, when the current block is a last block in a currentCTU, the circuitry enables deletion of, from among information on themotion vectors stored in the memory, information on a motion vector in aregion that will not be used in referencing performed in subsequent CTUprocessing.

This enables the decoder to reduce the amount of information to bestored in, for example, memory, by enabling deletion of information thatwill not be referenced in subsequent CTU processing.

For example, an encoding method according to one aspect of the presentdisclosure encodes a video and includes generating a motion vectorpredictor list by registering motion vector predictors obtained byreferencing a plurality of encoded blocks, selects one motion vectorpredictor from the motion vector predictor list, and implements aprediction mode that performs motion compensation using a motion vectorderived from the one motion vector predictor. The motion vectorpredictor list includes a spatially neighboring motion vector predictorobtained from a block spatially neighboring a current block, and aspatially broad motion vector predictor obtained from a block positionedat any of a plurality of predetermined positions in a second range thatis broader than a first range that spatially neighbors the currentblock. The plurality of predetermined positions are defined by a regularinterval using a top-left of a current picture as a reference point.

This enables the encoding method to achieve the same advantageouseffects as the encoder described above.

For example, a decoding method according to one aspect of the presentdisclosure decodes a video and includes generating a motion vectorpredictor list by registering motion vector predictors obtained byreferencing a plurality of decoded blocks, selects one motion vectorpredictor from the motion vector predictor list, and implements aprediction mode that performs motion compensation using a motion vectorderived from the one motion vector predictor. The motion vectorpredictor list includes a spatially neighboring motion vector predictorobtained from a block spatially neighboring a current block, and aspatially broad motion vector predictor obtained from a block positionedat any of a plurality of predetermined positions in a second range thatis broader than a first range that spatially neighbors the currentblock. The plurality of predetermined positions are defined by a regularinterval using a top-left of a current picture as a reference point.

This enables the decoding method to achieve the same advantageouseffects as the decoder described above.

Moreover, for example, the encoder according to one aspect of thepresent disclosure may include a splitter, an intra predictor, an interpredictor, a loop filter, a transformer, a quantizer, and an entropyencoder.

The splitter may split a picture into a plurality of blocks. The intrapredictor may perform intra prediction on a block included in theplurality of blocks. The inter predictor may perform inter prediction onthe block. The transformer may generate a transform coefficient bytransforming the prediction error between a prediction image obtained bythe intra prediction or inter prediction and the original image. Thequantizer may generate a quantized coefficient by quantizing thetransform coefficient. The entropy encoder may generate an encodedbitstream by encoding the quantized coefficient. The loop filter mayapply a filter to a reconstructed image of the block.

Moreover, for example, the encoder may be an encoder that encodes avideo including a plurality of pictures.

Then, the intra predictor may generate a motion vector predictor list byregistering motion vector predictors obtained by referencing a pluralityof encoded blocks, selects one motion vector predictor from the motionvector predictor list, and implements a prediction mode that performsmotion compensation using a motion vector derived from the one motionvector predictor. The motion vector predictor list may include aspatially neighboring motion vector predictor obtained from a blockspatially neighboring a current block, and a spatially broad motionvector predictor obtained from a block positioned at any of a pluralityof predetermined positions in a second range that is broader than afirst range that spatially neighbors the current block. Information onmotion vectors to be referenced in the prediction mode may be managed inassociation with reference blocks of a specific size. The plurality ofpredetermined positions may be positions of, from among the referenceblocks, reference blocks in positions defined by a regular intervalusing a current picture as a reference.

Moreover, for example, the decoder according to one aspect of thepresent disclosure may include an entropy decoder, an inverse quantizer,an inverse transformer, an intra predictor, an inter predictor, and aloop filter.

The entropy decoder may decode a quantized coefficient of a block in apicture from an encoded bitstream. The inverse quantizer may obtain atransform coefficient by inverse quantizing the quantized coefficient.The inverse transformer may obtain a prediction error by inversetransforming the transform coefficient. The intra predictor may performintra prediction on the block. The inter predictor may perform interprediction on the block. The filter may apply a filter to areconstructed image generated using a prediction image obtained by theintra prediction or the inter prediction and the prediction error.

Moreover, for example, the decoder may be a decoder that decodes a videoincluding a plurality of pictures.

Then, the intra predictor may generate a motion vector predictor list byregistering motion vector predictors obtained by referencing a pluralityof decoded blocks, selects one motion vector predictor from the motionvector predictor list, and implements a prediction mode that performsmotion compensation using a motion vector derived from the one motionvector predictor. The motion vector predictor list may include aspatially neighboring motion vector predictor obtained from a blockspatially neighboring a current block, and a spatially broad motionvector predictor obtained from a block positioned at any of a pluralityof predetermined positions in a second range that is broader than afirst range that spatially neighbors the current block. Information onmotion vectors to be referenced in the prediction mode may be managed inassociation with reference blocks of a specific size. The plurality ofpredetermined positions may be positions of, from among the referenceblocks, reference blocks in positions defined by a regular intervalusing a top-left of a current picture as a reference point.

Furthermore, these general and specific aspects may be implemented usinga system, a device, a method, an integrated circuit, a computer program,or a non-transitory computer-readable recording medium such as a CD-ROM,or any combination thereof.

Hereinafter, embodiments will be described with reference to thedrawings.

Note that the embodiments described below each show a general orspecific example. The numerical values, shapes, materials, components,the arrangement and connection of the components, steps, order of thesteps, etc., indicated in the following embodiments are mere examples,and therefore are not intended to limit the scope of the claims.Therefore, among the components in the following embodiments, those notrecited in any of the independent claims defining the broadest inventiveconcepts are described as optional components.

Embodiment 1

First, an outline of Embodiment 1 will be presented. Embodiment 1 is oneexample of an encoder and a decoder to which the processes and/orconfigurations presented in subsequent description of aspects of thepresent disclosure are applicable. Note that Embodiment 1 is merely oneexample of an encoder and a decoder to which the processes and/orconfigurations presented in the description of aspects of the presentdisclosure are applicable. The processes and/or configurations presentedin the description of aspects of the present disclosure can also beimplemented in an encoder and a decoder different from those accordingto Embodiment 1.

When the processes and/or configurations presented in the description ofaspects of the present disclosure are applied to Embodiment 1, forexample, any of the following may be performed.

-   -   (1) regarding the encoder or the decoder according to Embodiment        1, among components included in the encoder or the decoder        according to Embodiment 1, substituting a component        corresponding to a component presented in the description of        aspects of the present disclosure with a component presented in        the description of aspects of the present disclosure;    -   (2) regarding the encoder or the decoder according to Embodiment        1, implementing discretionary changes to functions or        implemented processes performed by one or more components        included in the encoder or the decoder according to Embodiment        1, such as addition, substitution, or removal, etc., of such        functions or implemented processes, then substituting a        component corresponding to a component presented in the        description of aspects of the present disclosure with a        component presented in the description of aspects of the present        disclosure;    -   (3) regarding the method implemented by the encoder or the        decoder according to Embodiment 1, implementing discretionary        changes such as addition of processes and/or substitution,        removal of one or more of the processes included in the method,        and then substituting a processes corresponding to a process        presented in the description of aspects of the present        disclosure with a process presented in the description of        aspects of the present disclosure;    -   (4) combining one or more components included in the encoder or        the decoder according to Embodiment 1 with a component presented        in the description of aspects of the present disclosure, a        component including one or more functions included in a        component presented in the description of aspects of the present        disclosure, or a component that implements one or more processes        implemented by a component presented in the description of        aspects of the present disclosure;    -   (5) combining a component including one or more functions        included in one or more components included in the encoder or        the decoder according to Embodiment 1, or a component that        implements one or more processes implemented by one or more        components included in the encoder or the decoder according to        Embodiment 1 with a component presented in the description of        aspects of the present disclosure, a component including one or        more functions included in a component presented in the        description of aspects of the present disclosure, or a component        that implements one or more processes implemented by a component        presented in the description of aspects of the present        disclosure;    -   (6) regarding the method implemented by the encoder or the        decoder according to Embodiment 1, among processes included in        the method, substituting a process corresponding to a process        presented in the description of aspects of the present        disclosure with a process presented in the description of        aspects of the present disclosure; and    -   (7) combining one or more processes included in the method        implemented by the encoder or the decoder according to        Embodiment 1 with a process presented in the description of        aspects of the present disclosure.

Note that the implementation of the processes and/or configurationspresented in the description of aspects of the present disclosure is notlimited to the above examples. For example, the processes and/orconfigurations presented in the description of aspects of the presentdisclosure may be implemented in a device used for a purpose differentfrom the moving picture/picture encoder or the moving picture/picturedecoder disclosed in Embodiment 1. Moreover, the processes and/orconfigurations presented in the description of aspects of the presentdisclosure may be independently implemented. Moreover, processes and/orconfigurations described in different aspects may be combined.

[Encoder Outline]

First, the encoder according to Embodiment 1 will be outlined. FIG. 1 isa block diagram illustrating a functional configuration of encoder 100according to Embodiment 1. Encoder 100 is a moving picture/pictureencoder that encodes a moving picture/picture block by block.

As illustrated in FIG. 1 , encoder 100 is a device that encodes apicture block by block, and includes splitter 102, subtractor 104,transformer 106, quantizer 108, entropy encoder 110, inverse quantizer112, inverse transformer 114, adder 116, block memory 118, loop filter120, frame memory 122, intra predictor 124, inter predictor 126, andprediction controller 128.

Encoder 100 is realized as, for example, a generic processor and memory.In this case, when a software program stored in the memory is executedby the processor, the processor functions as splitter 102, subtractor104, transformer 106, quantizer 108, entropy encoder 110, inversequantizer 112, inverse transformer 114, adder 116, loop filter 120,intra predictor 124, inter predictor 126, and prediction controller 128.Alternatively, encoder 100 may be realized as one or more dedicatedelectronic circuits corresponding to splitter 102, subtractor 104,transformer 106, quantizer 108, entropy encoder 110, inverse quantizer112, inverse transformer 114, adder 116, loop filter 120, intrapredictor 124, inter predictor 126, and prediction controller 128.

Hereinafter, each component included in encoder 100 will be described.

[Splitter]

Splitter 102 splits each picture included in an input moving pictureinto blocks, and outputs each block to subtractor 104. For example,splitter 102 first splits a picture into blocks of a fixed size (forexample, 128×128). The fixed size block is also referred to as codingtree unit (CTU). Splitter 102 then splits each fixed size block intoblocks of variable sizes (for example, 64×64 or smaller), based onrecursive quadtree and/or binary tree block splitting. The variable sizeblock is also referred to as a coding unit (CU), a prediction unit (PU),or a transform unit (TU). Note that in this embodiment, there is no needto differentiate between CU, PU, and TU; all or some of the blocks in apicture may be processed per CU, PU, or TU.

FIG. 2 illustrates one example of block splitting according toEmbodiment 1. In FIG. 2 , the solid lines represent block boundaries ofblocks split by quadtree block splitting, and the dashed lines representblock boundaries of blocks split by binary tree block splitting.

Here, block 10 is a square 128×128 pixel block (128×128 block). This128×128 block 10 is first split into four square 64×64 blocks (quadtreeblock splitting).

The top left 64×64 block is further vertically split into two rectangle32×64 blocks, and the left 32×64 block is further vertically split intotwo rectangle 16×64 blocks (binary tree block splitting). As a result,the top left 64×64 block is split into two 16×64 blocks 11 and 12 andone 32×64 block 13.

The top right 64×64 block is horizontally split into two rectangle 64×32blocks 14 and 15 (binary tree block splitting).

The bottom left 64×64 block is first split into four square 32×32 blocks(quadtree block splitting). The top left block and the bottom rightblock among the four 32×32 blocks are further split. The top left 32×32block is vertically split into two rectangle 16×32 blocks, and the right16×32 block is further horizontally split into two 16×16 blocks (binarytree block splitting). The bottom right 32×32 block is horizontallysplit into two 32×16 blocks (binary tree block splitting). As a result,the bottom left 64×64 block is split into 16×32 block 16, two 16×16blocks 17 and 18, two 32×32 blocks 19 and 20, and two 32×16 blocks 21and 22.

The bottom right 64×64 block 23 is not split.

As described above, in FIG. 2 , block 10 is split into 13 variable sizeblocks 11 through 23 based on recursive quadtree and binary tree blocksplitting. This type of splitting is also referred to as quadtree plusbinary tree (QTBT) splitting.

Note that in FIG. 2 , one block is split into four or two blocks(quadtree or binary tree block splitting), but splitting is not limitedto this example. For example, one block may be split into three blocks(ternary block splitting). Splitting including such ternary blocksplitting is also referred to as multi-type tree (MBT) splitting.

[Subtractor]

Subtractor 104 subtracts a prediction signal (prediction sample) from anoriginal signal (original sample) per block split by splitter 102. Inother words, subtractor 104 calculates prediction errors (also referredto as residuals) of a block to be encoded (hereinafter referred to as acurrent block). Subtractor 104 then outputs the calculated predictionerrors to transformer 106.

The original signal is a signal input into encoder 100, and is a signalrepresenting an image for each picture included in a moving picture (forexample, a luma signal and two chroma signals). Hereinafter, a signalrepresenting an image is also referred to as a sample.

[Transformer]

Transformer 106 transforms spatial domain prediction errors intofrequency domain transform coefficients, and outputs the transformcoefficients to quantizer 108. More specifically, transformer 106applies, for example, a predefined discrete cosine transform (DCT) ordiscrete sine transform (DST) to spatial domain prediction errors.

Note that transformer 106 may adaptively select a transform type fromamong a plurality of transform types, and transform prediction errorsinto transform coefficients by using a transform basis functioncorresponding to the selected transform type. This sort of transform isalso referred to as explicit multiple core transform (EMT) or adaptivemultiple transform (AMT).

The transform types include, for example, DCT-II, DCT-V, DCT-VIII,DST-I, and DST-VII. FIG. 3 is a chart indicating transform basisfunctions for each transform type. In FIG. 3 , N indicates the number ofinput pixels. For example, selection of a transform type from among theplurality of transform types may depend on the prediction type (intraprediction and inter prediction), and may depend on intra predictionmode.

Information indicating whether to apply such EMT or AMT (referred to as,for example, an AMT flag) and information indicating the selectedtransform type is signalled at the CU level. Note that the signaling ofsuch information need not be performed at the CU level, and may beperformed at another level (for example, at the sequence level, picturelevel, slice level, tile level, or CTU level).

Moreover, transformer 106 may apply a secondary transform to thetransform coefficients (transform result). Such a secondary transform isalso referred to as adaptive secondary transform (AST) or non-separablesecondary transform (NSST). For example, transformer 106 applies asecondary transform to each sub-block (for example, each 4×4 sub-block)included in the block of the transform coefficients corresponding to theintra prediction errors. Information indicating whether to apply NSSTand information related to the transform matrix used in NSST aresignalled at the CU level. Note that the signaling of such informationneed not be performed at the CU level, and may be performed at anotherlevel (for example, at the sequence level, picture level, slice level,tile level, or CTU level).

Here, a separable transform is a method in which a transform isperformed a plurality of times by separately performing a transform foreach direction according to the number of dimensions input. Anon-separable transform is a method of performing a collective transformin which two or more dimensions in a multidimensional input arecollectively regarded as a single dimension.

In one example of a non-separable transform, when the input is a 4×4block, the 4×4 block is regarded as a single array including 16components, and the transform applies a 16×16 transform matrix to thearray.

Moreover, similar to above, after an input 4×4 block is regarded as asingle array including 16 components, a transform that performs aplurality of Givens rotations on the array (i.e., a Hypercube-GivensTransform) is also one example of a non-separable transform.

[Quantizer]

Quantizer 108 quantizes the transform coefficients output fromtransformer 106. More specifically, quantizer 108 scans, in apredetermined scanning order, the transform coefficients of the currentblock, and quantizes the scanned transform coefficients based onquantization parameters (QP) corresponding to the transformcoefficients. Quantizer 108 then outputs the quantized transformcoefficients (hereinafter referred to as quantized coefficients) of thecurrent block to entropy encoder 110 and inverse quantizer 112.

A predetermined order is an order for quantizing/inverse quantizingtransform coefficients. For example, a predetermined scanning order isdefined as ascending order of frequency (from low to high frequency) ordescending order of frequency (from high to low frequency).

A quantization parameter is a parameter defining a quantization stepsize (quantization width). For example, if the value of the quantizationparameter increases, the quantization step size also increases. In otherwords, if the value of the quantization parameter increases, thequantization error increases.

[Entropy Encoder]

Entropy encoder 110 generates an encoded signal (encoded bitstream) byvariable length encoding quantized coefficients, which are inputs fromquantizer 108. More specifically, entropy encoder 110, for example,binarizes quantized coefficients and arithmetic encodes the binarysignal.

[Inverse Quantizer]

Inverse quantizer 112 inverse quantizes quantized coefficients, whichare inputs from quantizer 108. More specifically, inverse quantizer 112inverse quantizes, in a predetermined scanning order, quantizedcoefficients of the current block. Inverse quantizer 112 then outputsthe inverse quantized transform coefficients of the current block toinverse transformer 114.

[Inverse Transformer]

Inverse transformer 114 restores prediction errors by inversetransforming transform coefficients, which are inputs from inversequantizer 112. More specifically, inverse transformer 114 restores theprediction errors of the current block by applying an inverse transformcorresponding to the transform applied by transformer 106 on thetransform coefficients. Inverse transformer 114 then outputs therestored prediction errors to adder 116.

Note that since information is lost in quantization, the restoredprediction errors do not match the prediction errors calculated bysubtractor 104. In other words, the restored prediction errors includequantization errors.

[Adder]

Adder 116 reconstructs the current block by summing prediction errors,which are inputs from inverse transformer 114, and prediction samples,which are inputs from prediction controller 128. Adder 116 then outputsthe reconstructed block to block memory 118 and loop filter 120. Areconstructed block is also referred to as a local decoded block.

[Block Memory]

Block memory 118 is storage for storing blocks in a picture to beencoded (hereinafter referred to as a current picture) for reference inintra prediction. More specifically, block memory 118 storesreconstructed blocks output from adder 116.

[Loop Filter]

Loop filter 120 applies a loop filter to blocks reconstructed by adder116, and outputs the filtered reconstructed blocks to frame memory 122.A loop filter is a filter used in an encoding loop (in-loop filter), andincludes, for example, a deblocking filter (DF), a sample adaptiveoffset (SAO), and an adaptive loop filter (ALF).

In ALF, a least square error filter for removing compression artifactsis applied. For example, one filter from among a plurality of filters isselected for each 2×2 sub-block in the current block based on directionand activity of local gradients, and is applied.

More specifically, first, each sub-block (for example, each 2×2sub-block) is categorized into one out of a plurality of classes (forexample, 15 or 25 classes). The classification of the sub-block is basedon gradient directionality and activity. For example, classificationindex C is derived based on gradient directionality D (for example, 0 to2 or 0 to 4) and gradient activity A (for example, 0 to 4) (for example,C=5D+A). Then, based on classification index C, each sub-block iscategorized into one out of a plurality of classes (for example, 15 or25 classes).

For example, gradient directionality D is calculated by comparinggradients of a plurality of directions (for example, the horizontal,vertical, and two diagonal directions). Moreover, for example, gradientactivity A is calculated by summing gradients of a plurality ofdirections and quantizing the sum.

The filter to be used for each sub-block is determined from among theplurality of filters based on the result of such categorization.

The filter shape to be used in ALF is, for example, a circular symmetricfilter shape. FIG. 4A through FIG. 4C illustrate examples of filtershapes used in ALF. FIG. 4A illustrates a 5×5 diamond shape filter, FIG.4B illustrates a 7×7 diamond shape filter, and FIG. 4C illustrates a 9×9diamond shape filter. Information indicating the filter shape issignalled at the picture level. Note that the signaling of informationindicating the filter shape need not be performed at the picture level,and may be performed at another level (for example, at the sequencelevel, slice level, tile level, CTU level, or CU level).

The enabling or disabling of ALF is determined at the picture level orCU level. For example, for luma, the decision to apply ALF or not isdone at the CU level, and for chroma, the decision to apply ALF or notis done at the picture level. Information indicating whether ALF isenabled or disabled is signalled at the picture level or CU level. Notethat the signaling of information indicating whether ALF is enabled ordisabled need not be performed at the picture level or CU level, and maybe performed at another level (for example, at the sequence level, slicelevel, tile level, or CTU level).

The coefficients set for the plurality of selectable filters (forexample, 15 or 25 filters) is signalled at the picture level. Note thatthe signaling of the coefficients set need not be performed at thepicture level, and may be performed at another level (for example, atthe sequence level, slice level, tile level, CTU level, CU level, orsub-block level).

[Frame Memory]

Frame memory 122 is storage for storing reference pictures used in interprediction, and is also referred to as a frame buffer. Morespecifically, frame memory 122 stores reconstructed blocks filtered byloop filter 120.

[Intra Predictor]

Intra predictor 124 generates a prediction signal (intra predictionsignal) by intra predicting the current block with reference to a blockor blocks in the current picture and stored in block memory 118 (alsoreferred to as intra frame prediction). More specifically, intrapredictor 124 generates an intra prediction signal by intra predictionwith reference to samples (for example, luma and/or chroma values) of ablock or blocks neighboring the current block, and then outputs theintra prediction signal to prediction controller 128.

For example, intra predictor 124 performs intra prediction by using onemode from among a plurality of predefined intra prediction modes. Theintra prediction modes include one or more non-directional predictionmodes and a plurality of directional prediction modes.

The one or more non-directional prediction modes include, for example,planar prediction mode and DC prediction mode defined in theH.265/high-efficiency video coding (HEVC) standard (see NPL 1).

The plurality of directional prediction modes include, for example, the33 directional prediction modes defined in the H.265/HEVC standard. Notethat the plurality of directional prediction modes may further include32 directional prediction modes in addition to the 33 directionalprediction modes (for a total of 65 directional prediction modes). FIG.5A illustrates 67 intra prediction modes used in intra prediction (twonon-directional prediction modes and 65 directional prediction modes).The solid arrows represent the 33 directions defined in the H.265/HEVCstandard, and the dashed arrows represent the additional 32 directions.

Note that a luma block may be referenced in chroma block intraprediction. In other words, a chroma component of the current block maybe predicted based on a luma component of the current block. Such intraprediction is also referred to as cross-component linear model (CCLM)prediction. Such a chroma block intra prediction mode that references aluma block (referred to as, for example, CCLM mode) may be added as oneof the chroma block intra prediction modes.

Intra predictor 124 may correct post-intra-prediction pixel values basedon horizontal/vertical reference pixel gradients. Intra predictionaccompanied by this sort of correcting is also referred to as positiondependent intra prediction combination (PDPC). Information indicatingwhether to apply PDPC or not (referred to as, for example, a PDPC flag)is, for example, signalled at the CU level. Note that the signaling ofthis information need not be performed at the CU level, and may beperformed at another level (for example, on the sequence level, picturelevel, slice level, tile level, or CTU level).

[Inter Predictor]

Inter predictor 126 generates a prediction signal (inter predictionsignal) by inter predicting the current block with reference to a blockor blocks in a reference picture, which is different from the currentpicture and is stored in frame memory 122 (also referred to as interframe prediction). Inter prediction is performed per current block orper sub-block (for example, per 4×4 block) in the current block. Forexample, inter predictor 126 performs motion estimation in a referencepicture for the current block or sub-block. Inter predictor 126 thengenerates an inter prediction signal of the current block or sub-blockby motion compensation by using motion information (for example, amotion vector) obtained from motion estimation. Inter predictor 126 thenoutputs the generated inter prediction signal to prediction controller128.

The motion information used in motion compensation is signalled. Amotion vector predictor may be used for the signaling of the motionvector. In other words, the difference between the motion vector and themotion vector predictor may be signalled.

Note that the inter prediction signal may be generated using motioninformation for a neighboring block in addition to motion informationfor the current block obtained from motion estimation. Morespecifically, the inter prediction signal may be generated per sub-blockin the current block by calculating a weighted sum of a predictionsignal based on motion information obtained from motion estimation and aprediction signal based on motion information for a neighboring block.Such inter prediction (motion compensation) is also referred to asoverlapped block motion compensation (OBMC).

In such an OBMC mode, information indicating sub-block size for OBMC(referred to as, for example, OBMC block size) is signalled at thesequence level. Moreover, information indicating whether to apply theOBMC mode or not (referred to as, for example, an OBMC flag) issignalled at the CU level. Note that the signaling of such informationneed not be performed at the sequence level and CU level, and may beperformed at another level (for example, at the picture level, slicelevel, tile level, CTU level, or sub-block level).

Hereinafter, the OBMC mode will be described in further detail. FIG. 5Bis a flowchart and FIG. 5C is a conceptual diagram for illustrating anoutline of a prediction image correction process performed via OBMCprocessing.

First, a prediction image (Pred) is obtained through typical motioncompensation using a motion vector (MV) assigned to the current block.

Next, a prediction image (Pred_L) is obtained by applying a motionvector (MV_L) of the encoded neighboring left block to the currentblock, and a first pass of the correction of the prediction image ismade by superimposing the prediction image and Pred_L.

Similarly, a prediction image (Pred_U) is obtained by applying a motionvector (MV_U) of the encoded neighboring upper block to the currentblock, and a second pass of the correction of the prediction image ismade by superimposing the prediction image resulting from the first passand Pred_U. The result of the second pass is the final prediction image.

Note that the above example is of a two-pass correction method using theneighboring left and upper blocks, but the method may be a three-pass orhigher correction method that also uses the neighboring right and/orlower block.

Note that the region subject to superimposition may be the entire pixelregion of the block, and, alternatively, may be a partial block boundaryregion.

Note that here, the prediction image correction process is described asbeing based on a single reference picture, but the same applies when aprediction image is corrected based on a plurality of referencepictures. In such a case, after corrected prediction images resultingfrom performing correction based on each of the reference pictures areobtained, the obtained corrected prediction images are furthersuperimposed to obtain the final prediction image.

Note that the unit of the current block may be a prediction block and,alternatively, may be a sub-block obtained by further dividing theprediction block.

One example of a method for determining whether to implement OBMCprocessing is by using an obmc_flag, which is a signal that indicateswhether to implement OBMC processing. As one specific example, theencoder determines whether the current block belongs to a regionincluding complicated motion. The encoder sets the obmc_flag to a valueof “1” when the block belongs to a region including complicated motionand implements OBMC processing when encoding, and sets the obmc_flag toa value of “0” when the block does not belong to a region includingcomplication motion and encodes without implementing OBMC processing.The decoder switches between implementing OBMC processing or not bydecoding the obmc_flag written in the stream and performing the decodingin accordance with the flag value.

Note that the motion information may be derived on the decoder sidewithout being signalled. For example, a merge mode defined in theH.265/HEVC standard may be used. Moreover, for example, the motioninformation may be derived by performing motion estimation on thedecoder side. In this case, motion estimation is performed without usingthe pixel values of the current block.

Here, a mode for performing motion estimation on the decoder side willbe described. A mode for performing motion estimation on the decoderside is also referred to as pattern matched motion vector derivation(PMMVD) mode or frame rate up-conversion (FRUC) mode.

One example of FRUC processing is illustrated in FIG. 5D. First, acandidate list (a candidate list may be a merge list) of candidates eachincluding a motion vector predictor is generated with reference tomotion vectors of encoded blocks that spatially or temporally neighborthe current block. Next, the best candidate MV is selected from among aplurality of candidate MVs registered in the candidate list. Forexample, evaluation values for the candidates included in the candidatelist are calculated and one candidate is selected based on thecalculated evaluation values.

Next, a motion vector for the current block is derived from the motionvector of the selected candidate. More specifically, for example, themotion vector for the current block is calculated as the motion vectorof the selected candidate (best candidate MV), as-is. Alternatively, themotion vector for the current block may be derived by pattern matchingperformed in the vicinity of a position in a reference picturecorresponding to the motion vector of the selected candidate. In otherwords, when the vicinity of the best candidate MV is searched via thesame method and an MV having a better evaluation value is found, thebest candidate MV may be updated to the MV having the better evaluationvalue, and the MV having the better evaluation value may be used as thefinal MV for the current block. Note that a configuration in which thisprocessing is not implemented is also acceptable.

The same processes may be performed in cases in which the processing isperformed in units of sub-blocks.

Note that an evaluation value is calculated by calculating thedifference in the reconstructed image by pattern matching performedbetween a region in a reference picture corresponding to a motion vectorand a predetermined region. Note that the evaluation value may becalculated by using some other information in addition to thedifference.

The pattern matching used is either first pattern matching or secondpattern matching. First pattern matching and second pattern matching arealso referred to as bilateral matching and template matching,respectively.

In the first pattern matching, pattern matching is performed between twoblocks along the motion trajectory of the current block in two differentreference pictures. Therefore, in the first pattern matching, a regionin another reference picture conforming to the motion trajectory of thecurrent block is used as the predetermined region for theabove-described calculation of the candidate evaluation value.

FIG. 6 is for illustrating one example of pattern matching (bilateralmatching) between two blocks along a motion trajectory. As illustratedin FIG. 6 , in the first pattern matching, two motion vectors (MV0, MV1)are derived by finding the best match between two blocks along themotion trajectory of the current block (Cur block) in two differentreference pictures (Ref0, Ref1). More specifically, a difference between(i) a reconstructed image in a specified position in a first encodedreference picture (Ref0) specified by a candidate MV and (ii) areconstructed picture in a specified position in a second encodedreference picture (Ref1) specified by a symmetrical MV scaled at adisplay time interval of the candidate MV may be derived, and theevaluation value for the current block may be calculated by using thederived difference. The candidate MV having the best evaluation valueamong the plurality of candidate MVs may be selected as the final MV.

Under the assumption of continuous motion trajectory, the motion vectors(MV0, MV1) pointing to the two reference blocks shall be proportional tothe temporal distances (TD0, TD1) between the current picture (Cur Pic)and the two reference pictures (Ref0, Ref1). For example, when thecurrent picture is temporally between the two reference pictures and thetemporal distance from the current picture to the two reference picturesis the same, the first pattern matching derives a mirror basedbi-directional motion vector.

In the second pattern matching, pattern matching is performed between atemplate in the current picture (blocks neighboring the current block inthe current picture (for example, the top and/or left neighboringblocks)) and a block in a reference picture. Therefore, in the secondpattern matching, a block neighboring the current block in the currentpicture is used as the predetermined region for the above-describedcalculation of the candidate evaluation value.

FIG. 7 is for illustrating one example of pattern matching (templatematching) between a template in the current picture and a block in areference picture. As illustrated in FIG. 7 , in the second patternmatching, a motion vector of the current block is derived by searching areference picture (Ref0) to find the block that best matches neighboringblocks of the current block (Cur block) in the current picture (CurPic). More specifically, a difference between (i) a reconstructed imageof an encoded region that is both or one of the neighboring left andneighboring upper region and (ii) a reconstructed picture in the sameposition in an encoded reference picture (Ref0) specified by a candidateMV may be derived, and the evaluation value for the current block may becalculated by using the derived difference. The candidate MV having thebest evaluation value among the plurality of candidate MVs may beselected as the best candidate MV.

Information indicating whether to apply the FRUC mode or not (referredto as, for example, a FRUC flag) is signalled at the CU level. Moreover,when the FRUC mode is applied (for example, when the FRUC flag is set totrue), information indicating the pattern matching method (first patternmatching or second pattern matching) is signalled at the CU level. Notethat the signaling of such information need not be performed at the CUlevel, and may be performed at another level (for example, at thesequence level, picture level, slice level, tile level, CTU level, orsub-block level).

Here, a mode for deriving a motion vector based on a model assuminguniform linear motion will be described. This mode is also referred toas a bi-directional optical flow (BIO) mode.

FIG. 8 is for illustrating a model assuming uniform linear motion. InFIG. 8 , (v_(x), v_(y)) denotes a velocity vector, and τ₀ and τ₁ denotetemporal distances between the current picture (Cur Pic) and tworeference pictures (Ref₀, Ref₁). (MVx₀, MVy₀) denotes a motion vectorcorresponding to reference picture Ref₀, and (MVx₁, MVy₁) denotes amotion vector corresponding to reference picture Ref₁.

Here, under the assumption of uniform linear motion exhibited byvelocity vector (v_(x), v_(y)), (MVx₀, MVy₀) and (MVx₁, MVy₁) arerepresented as (v_(x)τ₀, v_(y)τ₀) and (−v_(x)τ₁, −v_(y)τ₁),respectively, and the following optical flow equation is given.MATH. 1∂I ^((k)) /∂t+v _(x) ∂I ^((k)) /∂x+v _(y) ∂I ^((k)) /∂y=0.  (1)

Here, I^((k)) denotes a luma value from reference picture k (k=0, 1)after motion compensation. This optical flow equation shows that the sumof (i) the time derivative of the luma value, (ii) the product of thehorizontal velocity and the horizontal component of the spatial gradientof a reference picture, and (iii) the product of the vertical velocityand the vertical component of the spatial gradient of a referencepicture is equal to zero. A motion vector of each block obtained from,for example, a merge list is corrected pixel by pixel based on acombination of the optical flow equation and Hermite interpolation.

Note that a motion vector may be derived on the decoder side using amethod other than deriving a motion vector based on a model assuminguniform linear motion. For example, a motion vector may be derived foreach sub-block based on motion vectors of neighboring blocks.

Here, a mode in which a motion vector is derived for each sub-blockbased on motion vectors of neighboring blocks will be described. Thismode is also referred to as affine motion compensation prediction mode.

FIG. 9A is for illustrating deriving a motion vector of each sub-blockbased on motion vectors of neighboring blocks. In FIG. 9A, the currentblock includes 16 4×4 sub-blocks. Here, motion vector v₀ of the top leftcorner control point in the current block is derived based on motionvectors of neighboring sub-blocks, and motion vector v₁ of the top rightcorner control point in the current block is derived based on motionvectors of neighboring blocks. Then, using the two motion vectors v₀ andv₁, the motion vector (v_(x), v_(y)) of each sub-block in the currentblock is derived using Equation 2 below.

$\begin{matrix}{\quad{{MATH}.\mspace{11mu} 2}} & \; \\\left\{ \begin{matrix}{v_{x} = {{\frac{\left( {v_{1x} - v_{0x}} \right)}{w}x} - {\frac{\left( {v_{1y} - v_{0y}} \right)}{w}y} + v_{0\; x}}} \\{v_{y} = {{\frac{\left( {v_{1y} - v_{0y}} \right)}{w}x} + {\frac{\left( {v_{1x} - v_{0x}} \right)}{w}y} + v_{0\; y}}}\end{matrix} \right. & (2)\end{matrix}$

Here, x and y are the horizontal and vertical positions of thesub-block, respectively, and w is a predetermined weighted coefficient.

Such an affine motion compensation prediction mode may include a numberof modes of different methods of deriving the motion vectors of the topleft and top right corner control points. Information indicating such anaffine motion compensation prediction mode (referred to as, for example,an affine flag) is signalled at the CU level. Note that the signaling ofinformation indicating the affine motion compensation prediction modeneed not be performed at the CU level, and may be performed at anotherlevel (for example, at the sequence level, picture level, slice level,tile level, CTU level, or sub-block level).

[Prediction Controller]

Prediction controller 128 selects either the intra prediction signal orthe inter prediction signal, and outputs the selected prediction signalto subtractor 104 and adder 116.

Here, an example of deriving a motion vector via merge mode in a currentpicture will be given. FIG. 9B is for illustrating an outline of aprocess for deriving a motion vector via merge mode.

First, an MV predictor list in which candidate MV predictors areregistered is generated. Examples of candidate MV predictors include:spatially neighboring MV predictors, which are MVs of encoded blockspositioned in the spatial vicinity of the current block; a temporallyneighboring MV predictor, which is an MV of a block in an encodedreference picture that neighbors a block in the same location as thecurrent block; a combined MV predictor, which is an MV generated bycombining the MV values of the spatially neighboring MV predictor andthe temporally neighboring MV predictor; and a zero MV predictor, whichis an MV whose value is zero.

Next, the MV of the current block is determined by selecting one MVpredictor from among the plurality of MV predictors registered in the MVpredictor list.

Furthermore, in the variable-length encoder, a merge_idx, which is asignal indicating which MV predictor is selected, is written and encodedinto the stream.

Note that the MV predictors registered in the MV predictor listillustrated in FIG. 9B constitute one example. The number of MVpredictors registered in the MV predictor list may be different from thenumber illustrated in FIG. 9B, the MV predictors registered in the MVpredictor list may omit one or more of the types of MV predictors givenin the example in FIG. 9B, and the MV predictors registered in the MVpredictor list may include one or more types of MV predictors inaddition to and different from the types given in the example in FIG.9B.

Note that the final MV may be determined by performing DMVR processing(to be described later) by using the MV of the current block derived viamerge mode.

Here, an example of determining an MV by using DMVR processing will begiven.

FIG. 9C is a conceptual diagram for illustrating an outline of DMVRprocessing.

First, the most appropriate MVP set for the current block is consideredto be the candidate MV, reference pixels are obtained from a firstreference picture, which is a picture processed in the L0 direction inaccordance with the candidate MV, and a second reference picture, whichis a picture processed in the L1 direction in accordance with thecandidate MV, and a template is generated by calculating the average ofthe reference pixels.

Next, using the template, the surrounding regions of the candidate MVsof the first and second reference pictures are searched, and the MV withthe lowest cost is determined to be the final MV. Note that the costvalue is calculated using, for example, the difference between eachpixel value in the template and each pixel value in the regionssearched, as well as the MV value.

Note that the outlines of the processes described here are fundamentallythe same in both the encoder and the decoder.

Note that processing other than the processing exactly as describedabove may be used, so long as the processing is capable of deriving thefinal MV by searching the surroundings of the candidate MV.

Here, an example of a mode that generates a prediction image by usingLIC processing will be given.

FIG. 9D is for illustrating an outline of a prediction image generationmethod using a luminance correction process performed via LICprocessing.

First, an MV is extracted for obtaining, from an encoded referencepicture, a reference image corresponding to the current block.

Next, information indicating how the luminance value changed between thereference picture and the current picture is extracted and a luminancecorrection parameter is calculated by using the luminance pixel valuesfor the encoded left neighboring reference region and the encoded upperneighboring reference region, and the luminance pixel value in the samelocation in the reference picture specified by the MV.

The prediction image for the current block is generated by performing aluminance correction process by using the luminance correction parameteron the reference image in the reference picture specified by the MV.

Note that the shape of the surrounding reference region illustrated inFIG. 9D is just one example; the surrounding reference region may have adifferent shape.

Moreover, although a prediction image is generated from a singlereference picture in this example, in cases in which a prediction imageis generated from a plurality of reference pictures as well, theprediction image is generated after performing a luminance correctionprocess, via the same method, on the reference images obtained from thereference pictures.

One example of a method for determining whether to implement LICprocessing is by using an lic_flag, which is a signal that indicateswhether to implement LIC processing. As one specific example, theencoder determines whether the current block belongs to a region ofluminance change. The encoder sets the lic_flag to a value of “1” whenthe block belongs to a region of luminance change and implements LICprocessing when encoding, and sets the lic_flag to a value of “0” whenthe block does not belong to a region of luminance change and encodeswithout implementing LIC processing. The decoder switches betweenimplementing LIC processing or not by decoding the lic_flag written inthe stream and performing the decoding in accordance with the flagvalue.

One example of a different method of determining whether to implementLIC processing is determining so in accordance with whether LICprocessing was determined to be implemented for a surrounding block. Inone specific example, when merge mode is used on the current block,whether LIC processing was applied in the encoding of the surroundingencoded block selected upon deriving the MV in the merge mode processingmay be determined, and whether to implement LIC processing or not can beswitched based on the result of the determination. Note that in thisexample, the same applies to the processing performed on the decoderside.

[Decoder Outline]

Next, a decoder capable of decoding an encoded signal (encodedbitstream) output from encoder 100 will be described. FIG. 10 is a blockdiagram illustrating a functional configuration of decoder 200 accordingto Embodiment 1. Decoder 200 is a moving picture/picture decoder thatdecodes a moving picture/picture block by block.

As illustrated in FIG. 10 , decoder 200 includes entropy decoder 202,inverse quantizer 204, inverse transformer 206, adder 208, block memory210, loop filter 212, frame memory 214, intra predictor 216, interpredictor 218, and prediction controller 220.

Decoder 200 is realized as, for example, a generic processor and memory.In this case, when a software program stored in the memory is executedby the processor, the processor functions as entropy decoder 202,inverse quantizer 204, inverse transformer 206, adder 208, loop filter212, intra predictor 216, inter predictor 218, and prediction controller220. Alternatively, decoder 200 may be realized as one or more dedicatedelectronic circuits corresponding to entropy decoder 202, inversequantizer 204, inverse transformer 206, adder 208, loop filter 212,intra predictor 216, inter predictor 218, and prediction controller 220.

Hereinafter, each component included in decoder 200 will be described.

[Entropy Decoder]

Entropy decoder 202 entropy decodes an encoded bitstream. Morespecifically, for example, entropy decoder 202 arithmetic decodes anencoded bitstream into a binary signal. Entropy decoder 202 thendebinarizes the binary signal. With this, entropy decoder 202 outputsquantized coefficients of each block to inverse quantizer 204.

[Inverse Quantizer]

Inverse quantizer 204 inverse quantizes quantized coefficients of ablock to be decoded (hereinafter referred to as a current block), whichare inputs from entropy decoder 202. More specifically, inversequantizer 204 inverse quantizes quantized coefficients of the currentblock based on quantization parameters corresponding to the quantizedcoefficients. Inverse quantizer 204 then outputs the inverse quantizedcoefficients (i.e., transform coefficients) of the current block toinverse transformer 206.

[Inverse Transformer]

Inverse transformer 206 restores prediction errors by inversetransforming transform coefficients, which are inputs from inversequantizer 204.

For example, when information parsed from an encoded bitstream indicatesapplication of EMT or AMT (for example, when the AMT flag is set totrue), inverse transformer 206 inverse transforms the transformcoefficients of the current block based on information indicating theparsed transform type.

Moreover, for example, when information parsed from an encoded bitstreamindicates application of NSST, inverse transformer 206 applies asecondary inverse transform to the transform coefficients.

[Adder]

Adder 208 reconstructs the current block by summing prediction errors,which are inputs from inverse transformer 206, and prediction samples,which is an input from prediction controller 220. Adder 208 then outputsthe reconstructed block to block memory 210 and loop filter 212.

[Block Memory]

Block memory 210 is storage for storing blocks in a picture to bedecoded (hereinafter referred to as a current picture) for reference inintra prediction. More specifically, block memory 210 storesreconstructed blocks output from adder 208.

[Loop Filter]

Loop filter 212 applies a loop filter to blocks reconstructed by adder208, and outputs the filtered reconstructed blocks to frame memory 214and, for example, a display device.

When information indicating the enabling or disabling of ALF parsed froman encoded bitstream indicates enabled, one filter from among aplurality of filters is selected based on direction and activity oflocal gradients, and the selected filter is applied to the reconstructedblock.

[Frame Memory]

Frame memory 214 is storage for storing reference pictures used in interprediction, and is also referred to as a frame buffer. Morespecifically, frame memory 214 stores reconstructed blocks filtered byloop filter 212.

[Intra Predictor]

Intra predictor 216 generates a prediction signal (intra predictionsignal) by intra prediction with reference to a block or blocks in thecurrent picture and stored in block memory 210. More specifically, intrapredictor 216 generates an intra prediction signal by intra predictionwith reference to samples (for example, luma and/or chroma values) of ablock or blocks neighboring the current block, and then outputs theintra prediction signal to prediction controller 220.

Note that when an intra prediction mode in which a chroma block is intrapredicted from a luma block is selected, intra predictor 216 may predictthe chroma component of the current block based on the luma component ofthe current block.

Moreover, when information indicating the application of PDPC is parsedfrom an encoded bitstream, intra predictor 216 correctspost-intra-prediction pixel values based on horizontal/verticalreference pixel gradients.

[Inter Predictor]

Inter predictor 218 predicts the current block with reference to areference picture stored in frame memory 214. Inter prediction isperformed per current block or per sub-block (for example, per 4×4block) in the current block. For example, inter predictor 218 generatesan inter prediction signal of the current block or sub-block by motioncompensation by using motion information (for example, a motion vector)parsed from an encoded bitstream, and outputs the inter predictionsignal to prediction controller 220.

Note that when the information parsed from the encoded bitstreamindicates application of OBMC mode, inter predictor 218 generates theinter prediction signal using motion information for a neighboring blockin addition to motion information for the current block obtained frommotion estimation.

Moreover, when the information parsed from the encoded bitstreamindicates application of FRUC mode, inter predictor 218 derives motioninformation by performing motion estimation in accordance with thepattern matching method (bilateral matching or template matching) parsedfrom the encoded bitstream. Inter predictor 218 then performs motioncompensation using the derived motion information.

Moreover, when BIO mode is to be applied, inter predictor 218 derives amotion vector based on a model assuming uniform linear motion. Moreover,when the information parsed from the encoded bitstream indicates thataffine motion compensation prediction mode is to be applied, interpredictor 218 derives a motion vector of each sub-block based on motionvectors of neighboring blocks.

[Prediction Controller]

Prediction controller 220 selects either the intra prediction signal orthe inter prediction signal, and outputs the selected prediction signalto adder 208.

[Description of Another Merge Mode Method]

FIG. 11 illustrates a generation method of a motion vector predictorlist in merge mode that uses spatially broad motion vector predictorsaccording to Embodiment 1. Unlike the method illustrated in FIG. 9B,with the method illustrated in FIG. 11 , encoder 100 does not merelyregister, in the motion vector predictor list, spatially neighboringmotion vector predictors obtained from blocks that neighbor the currentblock. With the method illustrated in FIG. 11 , encoder 100 obtainsspatially broad motion vector predictors by also referencing blockspositioned in a range that is broader than the positions of blocks thatneighbor the current block, and also registers the spatially broadmotion vector predictors in the motion vector predictor list. As usedherein, a motion vector predictor list is a list of motion vectors to beused in prediction, such as spatially neighboring motion vectorpredictors, registered by encoder 100 as motion vector predictors.Moreover, blocks referenced to obtain the spatially neighboring motionvector predictors and spatially broad motion vector predictors areprocessed blocks.

The size of the motion vector predictor list increases as the number ofmotion vectors that are motion vector predictor candidates forregistration in the motion vector predictor list increases. For example,as illustrated in FIG. 11 , the motion vector predictor list size is 10,which enables up to 10 motion vectors to be registered in the list.

As illustrated in FIG. 11 , the blocks to be referenced for obtainingspatially broad vector predictors are those positioned in a range thatis broader than the positions of blocks that neighbor the current block.Here, a range that is broader than the positions of the blocks thatneighbor the current block is a range defined by a predetermined numberof blocks based on the current block.

Encoder 100 then scans processed blocks positioned in the range that isbroader than the positions of the blocks that neighbor the currentblock, in order of proximity to the current block. When encoder 100 isable to obtain a motion vector by scanning processed blocks, encoder 100registers the value of the obtained motion vector into the motion vectorpredictor list as a spatially broad motion vector predictor. The valuesof motion vectors obtained by encoder 100 are registered in the motionvector predictor list by encoder 100 until a predetermined number ofvalues is reached. For example, in the example illustrated in FIG. 11 ,the spatially broad motion vector predictors are registered in themotion vector predictor list after the temporally neighboring motionvector predictor. In the example illustrated in FIG. 11 , threespatially broad motion vector predictors are registered in the motionvector predictor list.

As illustrated in FIG. 11 , by enabling encoder 100 to reference blockspositioned in a range that is broader than the positions of blocks thatneighbor the current block in the obtaining of motion vectors, encoder100 can obtain more suitable motion vector predictors compared to aconventional configuration. This is because the number of motion vectorsthat can be selected for registration in the motion vector predictorlist increase since the number of motion vectors subject to registrationas motion vector predictors increases beyond a conventionalconfiguration. With this, the possibility that the coding efficiency ofencoder 100 can be improved increases.

On the other hand, enabling encoder 100 to reference blocks positionedin a range that is broader than the positions of blocks that neighborthe current block in the obtaining of motion vectors increases theamount of information to be stored in, for example, memory. This isbecause it is necessary to store information on the motion vectors ofblocks that may potentially be referenced in, for example, memory. Sinceenabling encoder 100 to reference blocks positioned in a range that isbroader than the positions of blocks that neighbor the current block inthe obtaining of motion vectors increases the number of blocks that maypotentially be referenced, the amount of information to be stored byencoder 100 in, for example, memory, increases.

For example, consider a case in which the position of the current blockmoves one reference block over to the right. Here, a reference block isa block of a specific size that is treated as a unit reference. The sizeof the reference block may be, for example, 4×4 pixels. First, encoder100 stores, in, for example, memory, information held by each of blockspositioned in the range that is broader than the positions of the blocksthat neighbor the current block, in order of proximity to the currentblock. Next, when the position of the current block has moved onereference block to the right, each of the blocks positioned in a rangethat is broader than the positions of blocks that neighbor the currentblock is also moved one block to the right. Thus, encoder 100 also muststore, in, for example, memory, information held by each of blockspositioned in the range that is broader than the positions of the blocksthat neighbor the current block that have been moved one reference blockto the right. Thus, encoder 100 needs to store, in, for example, memory,information held by blocks positioned in a range that encompasses blocksthat may potentially be referenced, as blocks positioned in the rangethat is broader than the positions of the blocks that neighbor thecurrent block.

Note that the motion vector predictors registered in the motion vectorpredictor list described in FIG. 11 is merely one example. The number ofmotion vector predictors registered in the motion vector predictor listmay be different from the number described in FIG. 11 . Moreover, thetypes of motion vectors registered in the motion vector predictor listare not limited to the spatially neighboring motion vector predictor,the temporally neighboring motion vector predictor, the spatially broadmotion vector predictor, the combined motion vector predictor, and thezero motion vector predictor described in FIG. 11 . The types of motionvector predictors registered in the motion vector predictor list mayomit one or more of the types of motion vector predictors described inFIG. 11 . Additionally, the types of motion vector predictors registeredin the motion vector predictor list may additionally include types thatdiffer from those described in FIG. 11 .

Moreover, the positions and number of blocks referenced for obtainingmotion vector predictors described in FIG. 11 is merely one example; thepositions and number of blocks may be different from the positions andnumber of blocks described in FIG. 11 .

Moreover, the content described in FIG. 11 is described as applying toencoder 100, but the content may similarly apply to decoder 200.

Merge Mode Process Flow Example

FIG. 12 is a flow chart showing processes performed in merge mode thatuses spatially broad motion vector predictors according to Embodiment 1.

First, encoder 100 starts a loop that is performed per prediction block(step S1000).

Next, encoder 100 obtains spatially neighboring motion vector predictorsfrom blocks that neighbor the current block in current picture 25 (stepS1001).

Encoder 100 then obtains a temporally neighboring motion vectorpredictor from a block in a specific position in processed referencepicture 26 (step S1002).

Next, encoder 100 obtains spatially broad motion vector predictors byreferencing blocks (i) positioned in current picture 25 in a range thatis broader than the positions of blocks that neighbor the current blockand (ii) spaced apart by a predetermined interval (step S1003). Here,the predetermined interval may be determined using the top-left ofcurrent picture 25 as a reference point.

Encoder 100 then obtains motion vector predictors other than the motionvectors obtained in step S1001 through step S1003, such as combinedmotion vector predictors and zero motion vector predictors (step S1004).Encoder 100 registers the motion vector predictors obtained in stepS1001 through step S1004 in the motion vector predictor list. Theregistration of motion vector predictors into the motion vectorpredictor list may be performed in each of step S1001 through stepS1004, and may be performed collectively in, for example, step S1004.

Moreover, the motion vector predictors obtained by encoder 100 in stepS1001 through step S1004 may be rearranged by encoder 100 in accordancewith a specific condition, regardless of the order in which they wereobtained. Moreover, the motion vector predictors obtained by encoder 100in step S1001 through step S1004 may be, for example, combined, removed,or added by encoder 100, regardless of the order in which they wereobtained, and encoder 100 may reconfigure the motion vector predictorlist accordingly.

Note that the motion vector predictors described in step S1001 throughstep S1004 are merely one example; one or more of the motion vectorpredictors described in step S1001 through step S1004 may be omittedfrom the motion vector predictors obtained by encoder 100. Moreover, themotion vector predictors obtained by encoder 100 may additionallyinclude types of motion vector predictors other than those described instep S1001 through step S1004. Moreover, the motion vector predictorsobtained by encoder 100 need not be registered in the motion vectorpredictor list in the order described in step S1001 through step S1004;the motion vector predictors may be registered in the motion vectorpredictor list in an order different from the order described in stepS1001 through step S1004.

Next, encoder 100 selects a motion vector predictor to be assigned tothe current block in current picture 25 from among the obtained motionvector predictors (step S1005). Encoder 100 may select a motion vectorpredictor to be used in prediction from the motion vector predictorsregistered in the motion vector predictor list. Moreover, at this time,encoder 100 writes information indicating the selected motion vectorpredictor into the bitstream, and encodes it.

For example, encoder 100 uses the following method to select the motionvector predictor to be assigned to the current block. Encoder 100calculates the differences between provisional prediction imagesgenerated using motion vector predictors and input images to beprocessed. The encoder calculates evaluation values by calculating thedifferences, and selects a motion vector predictor candidate determinedto have the highest evaluation value as the motion vector predictor. Onthe other hand, decoder 200 decodes information indicating the motionvector predictor selected by encoder 100 to select the motion vectorpredictor to be assigned to the current block from among the pluralityof motion vector predictor candidates registered in the motion vectorpredictor list.

Next, encoder 100 derives a motion vector to be used in motioncompensation (MC), from the selected motion vector predictor (stepS1006). For example, encoder 100 use the selected motion vectorpredictor as the motion vector. Moreover, for example, encoder 100 mayperform, on an area in the vicinity of the selected motion vectorpredictor, a search process using a reconstructed image of a processedarea to update the motion vector predictor, and then use the updatedmotion vector predictor as the motion vector.

Next, encoder 100 generates a prediction image by performing motioncompensation (step S1007).

Encoder 100 then ends the loop that is performed per prediction block(step S1008). Here, encoder 100 concludes operations.

Note that the processes and flow of processes described in FIG. 12 aremerely one example; one or more of the processes described in FIG. 12may be omitted, a process not described in FIG. 12 may be added, and theorder of processes described in FIG. 12 may be rearranged.

Moreover, decoder 200 may perform the operations from step S1000 to stepS1008 described in FIG. 12 by switching encoding with decoding. Notethat the operation described as “encoded in the bitstream” in theencoding can be replaced with “decoded from the bitstream” in thedecoding.

FIG. 13 illustrates a first method of referencing spatially broadvectors in merge mode that uses spatially broad motion vector predictorsaccording to Embodiment 1. In FIG. 13 , the operations performed in stepS1003 described in FIG. 12 are explained in detail.

In the example illustrated in FIG. 13 , the 8×8 pixel current block 31is positioned in the most top-left position in current CTU (Coding TreeUnit) 30. FIG. 13 shows the positions of reference blocks to bereferenced upon processing current block 31 positioned in the mosttop-left position in current CTU 30. This referencing is performed bythe encoder in order for encoder 100 to obtain spatially neighboringmotion vector predictors and spatially broad motion vector predictors.Moreover, the motion vector predictors to be referenced are defined per4×4 pixel reference block, which is the smallest prediction block unit.

Like the example described in FIG. 11 , encoder 100 obtains spatiallyneighboring motion vector predictors by referencing, on a per referenceblock basis, processed blocks that spatially neighbor current block 31.In FIG. 13 , processed blocks that spatially neighbor current block 31are illustrated as hatched blocks. On the other hand, encoder 100obtains spatially broad motion vector predictors by referencing blocks(i) positioned in a range that is broader than the positions of blocksthat neighbor current block 31 and (ii) spaced apart by a predeterminedinterval. As illustrated in FIG. 13 , blocks marked with an X indicatethe blocks (i) positioned in a range that is broader than the positionsof blocks that neighbor current block 31 and (ii) spaced apart by apredetermined interval. The predetermined interval is four referenceblocks in the horizontal direction and four reference blocks in thevertical direction. In other words, the predetermined interval is 16pixels in the horizontal direction and 16 pixels in the verticaldirection.

Each block that is marked with an X and hatched is, from among processedblocks (i) positioned in a range that is broader than the positions ofblocks that neighbor current block 31 and (ii) spaced apart by apredetermined interval, a block that meets the following conditions: (1)is positioned outside of current block 31, and (2) is one of foursequential reference blocks in any one of the down, left-down, left,left-up, up, right-up, and right directions, from at least one ofreference blocks that are closest to current block 31 from amongreference blocks that are spaced apart by the predetermined interval andcover the top and left sides of current block 31. In other words, eachblock that is marked with an X and hatched indicates, from amongprocessed blocks (i) positioned in a range that is broader than thepositions of blocks that neighbor current block 31 and (ii) spaced apartby the predetermined interval, a block that is positioned outside of thecurrent block and within a range spreading radially outward, up to fourof the above blocks, from a position of a closest one of blocks thatsurround the left and top sides of current block 31.

The range of blocks that are marked with an X and hatched may beadaptively switched based on the capability of the encoder or the sizeof the current picture. Moreover, the predetermined interval betweenblocks that are marked with an X and hatched may be adaptively switchedbased on the capability of the encoder or the size of the currentpicture.

Encoder 100 then scans the blocks marked with an X and hatched in FIG.13 in order of proximity to current block 31, and obtains the motionvector values from the scanned blocks. Encoder 100 registers the valuesof the obtained motion vectors into the motion vector predictor list asspatially broad motion vector predictors, until a specific number isreached.

FIG. 14 illustrates a second method of referencing spatially broadvectors in merge mode that uses spatially broad motion vector predictorsaccording to Embodiment 1. FIG. 14 illustrates positions of referenceblocks for obtaining spatially neighboring motion vector predictors andspatially broad motion vector predictors when current block 31 a is in adifferent position than current block 31 illustrated in FIG. 13 .Specifically, current block 31 a is an 8×16 pixel region that ispositioned in the central upper area of current CTU 30.

Like with the method described in FIG. 13 , encoder 100 obtainsspatially neighboring motion vector predictors by referencing processedblocks that spatially neighbor current block 31 a. The processed blocksthat spatially neighbor current block 31 a, which are to be referencedby encoder 100, are, for example, the reference blocks indicated ashatched blocks in FIG. 14 .

Moreover, like with the method described in FIG. 13 , encoder 100obtains spatially broad motion vector predictors by referencingprocessed blocks (i) positioned in a range that is broader than thepositions of blocks that neighbor current block 31 a and (ii) spacedapart by a predetermined interval. In FIG. 14 , among processed blocks(i) positioned in a range that is broader than the positions of blocksthat neighbor current block 31 a and (ii) spaced apart by apredetermined interval, the blocks to be referenced by encoder 100 arethe blocks that are marked with an X and hatched. Each block that ismarked with an X and hatched is, from among processed blocks (i)positioned in a range that is broader than the positions of blocks thatneighbor current block 31 a and (ii) spaced apart by a predeterminedinterval, a block that meets the following conditions: (1) is positionedoutside of current block 31 a, and (2) is one of four sequentialreference blocks in any one of the down, left-down, left, left-up, up,right-up, and right directions, from at least one of reference blocksthat are closest to current block 31 a from among reference blocks thatare spaced apart by the predetermined interval and cover the top andleft sides of current block 31 a. In other words, each block that ismarked with an X and hatched indicates, from among processed blocks (i)positioned in a range that is broader than the positions of blocks thatneighbor current block 31 a and (ii) spaced apart by the predeterminedinterval, a block that is positioned outside of the current block andwithin a range spreading radially outward, up to four of the aboveblocks, from a position of a closest one of blocks that surround theleft and top sides of current block 31 a.

Encoder 100 then scans the blocks marked with an X and hatched in FIG.14 in order of proximity to current block 31 a, and obtains the motionvector values from the scanned blocks. Encoder 100 registers the valuesof the obtained motion vectors into the motion vector predictor list asspatially broad motion vector predictors, until a specific number isreached. Moreover, the blocks are reference blocks. Note that thepredetermined interval is four reference blocks in the horizontaldirection and four reference blocks in the vertical direction. In otherwords, the predetermined interval is 16 pixels in the horizontaldirection and 16 pixels in the vertical direction.

Note that among the blocks that are marked with an X, hatched, andpositioned in the current CTU, those that come after current block 31 ain processing order by encoder 100 cannot be referenced by encoder 100for the obtaining of a motion vector predictor. This is because themotion vectors of blocks that come after current block 31 a inprocessing order by encoder 100 are undefined at the point in time thatencoder 100 processes current block 31 a.

The positions of blocks marked with an X and hatched in the exampleillustrated in FIG. 14 have moved from the example illustrated in FIG.13 . However, blocks marked with an X and hatched in FIG. 14 have notmoved to positions other than blocks marked with an X in FIG. 13 . Inother words, regardless of the position and size of the current block,in both FIG. 13 and FIG. 14 , reference blocks, which are blocks markedwith an X, are referenced by encoder 100.

In the example described in FIG. 11 , since blocks positioned in a rangethat is broader than the range of positions of blocks that neighborcurrent block 27 are referenced based on their relative position tocurrent block 27, taking into consideration the sequential movement ofthe position of the current block, there is a possibility that themotion vectors for all block positions will be referenced. Accordingly,encoder 100 must store, in, for example, memory, information on themotion vectors for all block positions. However, with the methodaccording to the present embodiment described in FIG. 13 and FIG. 14 ,since processed blocks that are spaced apart by a predetermined intervalare referenced, it is sufficient if encoder 100 stores, in, for example,memory, the information for blocks in limited positions. Accordingly,encoder 100 can reduce the amount of information to be stored, whichmakes it possible to significantly reduce the capacity of, for example,memory. As such, encoder 100 allows for a reduction in the scale of thecircuitry included in encoder 100.

FIG. 15 illustrates a third method of referencing spatially broadvectors in merge mode that uses spatially broad motion vector predictorsaccording to Embodiment 1. FIG. 15 illustrates positions of referenceblocks for obtaining spatially neighboring motion vector predictors andspatially broad motion vector predictors when current block 31 b is in adifferent position than current block 31 illustrated in FIG. 13 andcurrent block 31 a illustrated in FIG. 14 . Specifically, current block31 b is a 32×32 pixel region that is positioned in the bottom-rightvicinity of current CTU 30.

Like with the methods described in FIG. 13 and FIG. 14 , encoder 100obtains spatially neighboring motion vector predictors by referencingprocessed blocks that spatially neighbor current block 31 b. Theprocessed blocks that spatially neighbor current block 31 b, which areto be referenced by encoder 100, are, for example, the reference blocksindicated as hatched blocks in FIG. 15 .

Moreover, like with the methods described in FIG. 13 and FIG. 14 ,encoder 100 obtains spatially broad motion vector predictors byreferencing processed blocks (i) positioned in a range that is broaderthan the positions of blocks that neighbor current block 31 b and (ii)spaced apart by a predetermined interval. In FIG. 15 , among processedblocks (i) positioned in a range that is broader than the positions ofblocks that neighbor current block 31 b and (ii) spaced apart by apredetermined interval, the blocks to be referenced by encoder 100 arethe blocks that are marked with an X and hatched. Each block that ismarked with an X and hatched is, from among processed blocks (i)positioned in a range that is broader than the positions of blocks thatneighbor current block 31 b and (ii) spaced apart by a predeterminedinterval, a block that meets the following conditions: (1) is positionedoutside of current block 31 b, and (2) is one of four sequentialreference blocks in any one of the down, left-down, left, left-up, up,right-up, and right directions, from at least one of reference blocksthat are closest to current block 31 b from among reference blocks thatare spaced apart by the predetermined interval and cover the top andleft sides of current block 31 b. In other words, each block that ismarked with an X and hatched indicates, from among processed blocks (i)positioned in a range that is broader than the positions of blocks thatneighbor current block 31 b and (ii) spaced apart by the predeterminedinterval, a block that is positioned outside of the current block andwithin a range spreading radially outward, up to four of the aboveblocks, from a position of a closest one of blocks that surround theleft and top sides of current block 31 b.

Encoder 100 then scans the blocks marked with an X and hatched in FIG.15 in order of proximity to current block 31 b, and obtains the motionvector values from the scanned blocks. Encoder 100 registers the valuesof the obtained motion vectors into the motion vector predictor list asspatially broad motion vector predictors, until a specific number isreached. Moreover, the blocks are reference blocks. Note that thepredetermined interval is four reference blocks in the horizontaldirection and four reference blocks in the vertical direction. In otherwords, the predetermined interval is 16 pixels in the horizontaldirection and 16 pixels in the vertical direction.

Since current block 31 b is larger than current block 31 and currentblock 31 a, the method described in FIG. 15 differs from the methodsdescribed in FIG. 13 and FIG. 14 in that only a portion of the blocksmarked with an X are allowed to be referenced. Specifically, rather thanallowing all of the blocks marked with an X that are on the left and topsides of current block 31 b to be referenced, only a portion of theblocks marked with an X that are on the left and top sides of currentblock 31 b are allowed to be referenced. For example, the sequences ofblocks to be referenced that extend left of current block 31 b arelimited to three sequences, the sequences of blocks to be referencedthat extend upward of current block 31 b are limited to three sequences,and sequences of blocks other than the sequences of blocks selected asreference candidates by encoder 100 are not referenced by encoder 100.

This prevents increases and decreases in the number of referencecandidate blocks, depending on the size of the current block. Inparticular, this prevents, for example, an extreme increase in thenumber of reference candidate blocks, depending on the size of thecurrent block. As such, encoder 100 allows for the homogenization ofprocessing amount and the scale of the circuitry included in encoder100.

Note that the predetermined interval illustrated in FIG. 13 , FIG. 14 ,and FIG. 15 is merely one example. The predetermined interval isexemplified as four reference blocks, but the number of reference blocksthat define the predetermined interval is not limited to four. Thenumber of reference blocks that define the predetermined interval may besome other number. Moreover, the predetermined interval need notnecessarily be defined by a number of reference blocks or pixels. Thepredetermined interval may be defined by some method other than a methodusing a number of reference blocks or pixels.

Note that the method of selecting blocks marked with an X and hatched inFIG. 13 , FIG. 14 , and FIG. 15 is merely one example. The method ofselecting blocks marked with an X and hatched is not limited to themethod illustrated in FIG. 13 , FIG. 14 , and FIG. 15 ; blocks markedwith an X and hatched may be selected using a method other than themethod illustrated in FIG. 13 , FIG. 14 , and FIG. 15 .

Note that in FIG. 13 , FIG. 14 , and FIG. 15 , blocks neighboring thetop-left of current block 31 are neighboring blocks of current block 31,but may be selected by encoder 100 as blocks to be referenced to obtainspatially broad motion vector predictors.

Moreover, decoder 200 may perform the content described in FIG. 13through FIG. 15 by switching encoding with decoding. Note that theoperation described as “encoded in the bitstream” in the encoding can bereplaced with “decoded from the bitstream” in the decoding.

FIG. 16 is a flow chart showing a management method for memory, etc.,that stores motion vectors for referencing spatially broad motion vectorpredictors according to an embodiment. The management method describedin FIG. 16 applies to both encoder 100 and decoder 200.

Information on motion vectors for referencing spatially broad motionvector predictors described in FIG. 12 through FIG. 15 is stored inmemory, etc., in encoder 100 or decoder 200.

Hereinafter, the flow of processes performed in encoder 100 will bedescribed.

First, encoder 100 derives the motion vector of current block 27, andperforms a prediction process (step S2000). Encoder 100 may readinformation on the motion vector stored in, for example, memory, toderive the motion vector of current block 27 and perform a predictionprocess.

Next, encoder 100 determines whether current block 27 includes one ofpixel positions spaced apart by a predetermined interval using thetop-left of current picture 25 as a reference point (step S2001). Pixelpositions spaced apart by a predetermined interval using the top-left ofcurrent picture 25 as a reference point correspond to the blocks markedwith an X in FIG. 13 through FIG. 15 .

When encoder 100 determines that current block 27 includes one of pixelpositions spaced apart by a predetermined interval using the top-left ofcurrent picture 25 as a reference point (yes in step S2001), encoder 100stores, in, for example, memory, motion vector information on currentblock 27 (step S2002).

When encoder 100 determines that current block 27 does not include oneof pixel positions spaced apart by a predetermined interval using thetop-left of current picture 25 as a reference point (no in step S2001),encoder 100 does not store, in, for example, memory, motion vectorinformation on current block 27.

Next, encoder 100 determines whether current block 27 is the last blockin the current CTU (step S2003).

When encoder 100 determines that current block 27 is the last block inthe current CTU (yes in step S2003), encoder 100 clears the memoryregion in which information on the motion vectors at positions of blocksthat will not be referenced in subsequent CTU processing, from amonginformation on motion vectors for referencing spatially broad motionvector predictors that is stored in, for example, memory (step S2004).In other words, from among information stored in, for example, memory,on motion vectors for referencing spatially broad motion vectorpredictors, encoder 100 deletes information on motion vectors atpositions of blocks that will not be referenced in subsequent CTUprocessing, from the respective memory regions. This enables encoder 100to store, in, for example, the cleared storage region, information onmotion vectors derived in subsequent CTU processing.

When encoder 100 determines that current block 27 is not the last blockin the current CTU (no in step S2003), encoder 100 does not clear thememory region in which information on the motion vectors at positions ofblocks that will not be referenced in subsequent CTU processing, fromamong information on motion vectors for referencing spatially broadmotion vector predictors that is stored in, for example, memory. Inother words, from among information stored in, for example, memory, onmotion vectors for referencing spatially broad motion vector predictors,encoder 100 does not delete information on motion vectors at positionsof blocks that will not be referenced in subsequent CTU processing, fromthe respective memory regions.

Here, encoder 100 concludes operations.

Accordingly, encoder 100 can manage memory regions efficiently with asimple management method. As such, encoder 100 increases the probabilityof being able to reduce the scale of the circuitry and storage region ofmemory, etc., included in encoder 100.

Note that the processes and flow of processes described in FIG. 16 aremerely one example; one or more of the processes described in FIG. 16may be omitted, a process not described in FIG. 16 may be added, and theorder of processes described in FIG. 16 may be rearranged.

Moreover, decoder 200 may perform the operations from step S2000 to stepS1004 described in FIG. 16 by switching encoding with decoding.

With the configuration described in FIG. 12 through FIG. 16 , in thegeneration of a motion vector predictor list in merge mode, encoder 100or decoder 200 enable the following. Upon referencing motion vectorpredictors, encoder 100 or decoder 200 can restrict the referencing toprocessed blocks (i) positioned in a range that is broader than therange of positions of blocks that neighbor current block 27 and (ii)spaced apart by a predetermined interval using the top-left of currentpicture 25 as a reference point. This makes it possible for encoder 100to significantly reduce the amount of information to be stored in, forexample, memory, on motion vectors used for referencing spatially broadmotion vector predictors obtained as motion vector predictors.Accordingly, encoder 100 or decoder 200 allows for a reduction in thescale of the circuitry included in encoder 100 or decoder 200.

Variation

The variation described hereinafter applies to both encoder 100 anddecoder 200. Hereinafter, the content of, for example, processesdescribed with reference to encoder 100 can be applied to processesperformed by decoder 200 by reading “encoder 100” as “decoder 200”.

Encoder 100 may apply the processes described in this embodiment to aprediction mode other than merge mode for performing a predictionprocess using the motion vector predictor list. Specifically, encoder100 may use the processes described in this embodiment in the generationor usage, etc., of a motion vector predictor list used for derivingmotion vector predictors in normal inter mode, or in the generation orusage, etc., of a candidate motion vector list for specifying motionvectors in FRUC mode. This makes it possible to, in prediction modesother than merge mode as well, obtain motion vector predictors andderive motion vectors more efficiently than conventional methods, byreferencing blocks, while also reducing the scale of circuitry includedin encoder 100. In other words, the possibility that the codingefficiency of encoder 100 can be improved in a plurality of predictionmodes increases.

Note that the spatially broad motion vector predictors according to thepresent disclosure may be motion vector predictors obtained by encoder100 by referencing, from among blocks positioned inside current picture25, blocks other than blocks that spatially neighbor current block 27.Moreover, the spatially broad motion vector predictors may be motionvector predictors obtained by encoder 100 by referencing blocks thatspatially neighbor current block 27, excluding blocks referenced for thepurpose of obtaining spatially neighboring motion vector predictors.

Note that the spatially broad motion vector predictors according to thisembodiment may be determined as follows. First, encoder 100 determines afirst block made up of a plurality of blocks in current picture 25.Here, the first block is a block positioned in the area spatiallysurrounding current block 27, and may be a block including one of pixelpositions determined using a predetermined pixel position in currentpicture 25 as a reference point by encoder 100. Specifically, asillustrated in FIG. 13 through FIG. 15 , the first block may be a blockincluding one of pixel positions spaced apart by a predeterminedinterval, using the top-left pixel position of current picture 25 as areference point. Moreover, in such cases, the first block may be thesame in all blocks in current picture 25.

Moreover, for example, encoder 100 may determine the first blocks to beblocks including one of pixel positions spaced apart by a predetermineddistance using the top-left pixel in the current CTU including currentblock 27 as a reference point. In such cases, the first block may be thesame in all blocks included in the current CTU. In other words, encoder100 may determine all same blocks among the plurality of blocks incurrent picture 25 to be the first block.

Next, encoder 100 determines a second block from among the first blocks.Here, the second block is a block determined based on current block 27,from among first blocks, and may be a block that precedes current block27 in processing order by encoder 100. Specifically, as illustrated inFIG. 13 through FIG. 15 , the second block may be a block positionedwithin a given range determined based on the position of the blockclosest to current block 27 from among blocks positioned in thesurrounding area of the left and top edges of current block 27.Moreover, for example, the second block may be a block within the givenrange determined based on the position of the current CTU includingcurrent block 27. In such cases, the second block may be the same in allblocks included in the current CTU.

Next, encoder 100 obtains a motion vector by referring to a secondblock, and registers the obtained motion vector in the prediction motionvector list as a spatially broad prediction motion vector for currentblock 27.

Note that in the determining of spatially broad motion vectorpredictors, blocks that may potentially be referenced for obtainingspatially broad motion vector predictors in current picture 25 may bedefined as third blocks. In such cases, encoder 100 may determine aplurality of first blocks from the plurality of third blocks.Specifically, blocks that precede current block 27 in processing orderby encoder 100 may be determined to be third blocks. Then, among thethird blocks, blocks including pixel positions determined based onpredetermined pixel positions in current picture 25 may be determined tobe first blocks, as illustrated in FIG. 13 through FIG. 15 . Here,encoder 100 need not store information on the motion vectors for allthird blocks in, for example, memory; it is sufficient if encoder 100stores the motion vector information on the first blocks in, forexample, memory

[Implementation]

FIG. 17 is a block diagram illustrating an implementation example of anencoder according to Embodiment 1. Encoder 100 includes circuitry 150and memory 152. For example, the plurality of elements included inencoder 100 illustrated in FIG. 1 are implemented as circuitry 150 andmemory 152 illustrated in FIG. 17 .

Circuitry 150 is electronic circuitry that is capable of accessingmemory 152, and performs information processing. For example, circuitry150 is dedicated or generic electronic circuitry that encodes a videousing memory 152. Circuitry 150 may be a processor such as a CPU.Moreover, circuitry 150 may be an aggregate of a plurality of electroniccircuits.

Moreover, for example, circuitry 150 may perform the roles of aplurality of elements from among the plurality of elements included inencoder 100 illustrated in FIG. 1 , excluding elements for storinginformation. In other words, circuitry 150 may performed theabove-described operations as the operations performed by thoseelements.

Memory 152 is dedicated or generic memory that stores information forcircuitry 150 to encode a video. Memory 152 may be electronic circuitry,may be coupled to circuitry 150, and may be included in circuitry 150.

Moreover, memory 152 may be an aggregate of a plurality of electroniccircuits, and may be configured of a plurality of sub-memories.Moreover, memory 152 may be, for example, a magnetic disk or an opticaldisk, and may be realized as storage or a recording medium, for example.Moreover, memory 152 may be nonvolatile memory, and may be volatilememory.

For example, memory 152 may perform the roles of, from among theplurality of elements included in encoder 100 illustrated in FIG. 1 ,those for storing information.

Moreover, memory 152 may store an encoded video, and may store asequence of bits corresponding to an encoded video. Moreover, memory 152may store a program for circuitry 150 to encode a video.

Note that not all of the plurality of elements illustrated in FIG. 1need to be implemented in encoder 100, and not all of theabove-described processes need to be performed. Some of the plurality ofelements illustrated in FIG. 1 may be included in some other device, andsome of the above-described processes may be executed by some otherdevice. Then, due to some of the plurality of elements illustrated inFIG. 1 being implemented in encoder 100 and some of the above-describedprocesses being performed by encoder 100, information related to videoencoding can be appropriately configured.

FIG. 18 is a flow chart illustrating an example of operations performedby an encoder according to Embodiment 1. For example, encoder 100illustrated in FIG. 17 performs the processes illustrated in FIG. 18upon performing prediction in merge mode. Specifically, circuitry 150performs the following operations using memory 152.

First, encoder 100 generates a motion vector predictor list byregistering spatially neighboring motion vector predictors and spatiallybroad motion vector predictors (step S3001).

Next, encoder 100 selects one motion vector predictor from the motionvector predictor list (step S3002).

Encoder 100 then performs motion compensation on current block 27 usinga motion vector derived from the motion vector predictor (step S3003).

The processes illustrated in S3001 through S3003 and performed byencoder 100 may be performed in merge mode.

Moreover, encoder 100 may define blocks (i) positioned in a range thatis broader than the range of positions of blocks that neighbor currentblock 27 and (ii) spaced apart by a predetermined interval as referenceblocks having a specific size. Moreover, information on motion vectorsto be referenced by encoder 100 may be managed in association with thereference blocks.

Moreover, encoder 100 may be capable of adaptively switching, based onthe capability of encoder 100 or the size, etc., of current picture 25,the range of blocks positioned in a range that is broader than the rangeof positions of blocks that neighbor current block 27. Moreover, encoder100 may be capable of adaptively switching, based on the capability ofencoder 100 or the size, etc., of current picture 25, the predeterminedinterval that the blocks are spaced apart by.

Moreover, encoder 100 may write, into the slice, picture, or sequenceheader, information specifying the predetermined interval of the blocks(i) positioned in a range that is broader than the range of positions ofblocks that neighbor current block 27 and (ii) spaced apart by apredetermined interval, or the range of positions of the blocks (i)positioned in a range that is broader than the range of positions ofblocks that neighbor current block 27 and (ii) spaced apart by apredetermined interval.

For example, when the capability of encoder 100 is a first capabilitythat is lower than a first reference, the predetermined interval of theblocks (i) positioned in a range that is broader than the range ofpositions of blocks that neighbor current block 27 and (ii) spaced apartby a predetermined interval may be a first interval, and when thecapability of encoder 100 is a second capability that is higher than thefirst reference, the predetermined interval may be a second intervalthat is narrower than the first interval. In other words, when thecapability of encoder 100 is lower than a reference, encoder 100 maynarrow the predetermined interval of blocks (i) positioned in a rangethat is broader than the range of positions of blocks that neighborcurrent block 27 and (ii) spaced apart by a predetermined interval.Moreover, when the capability of encoder 100 is higher than a reference,encoder 100 may widen the predetermined interval of blocks (i)positioned in a range that is broader than the range of positions ofblocks that neighbor current block 27 and (ii) spaced apart by apredetermined interval.

Moreover, for example, when the capability of encoder 100 is a thirdcapability that is lower than a second reference, the number ofreference blocks in predetermined positions to be referenced for motionvector predictor list generation in a range that is broader than therange of positions of blocks neighboring current block 27 may be a firstnumber, and when the capability of encoder 100 is a fourth capabilitythat is higher than the second reference, the number of reference blocksin predetermined positions to be referenced for motion vector predictorlist generation in a range that is broader than the range of positionsof blocks neighboring current block 27 may be a second number that isgreater than the first number. In other words, when the capability ofencoder 100 is lower than a reference, encoder 100 may reduce the numberof reference blocks in a range that is broader than the range ofpositions of blocks that neighbor current block 27. Moreover, when thecapability of encoder 100 is higher than a reference, encoder 100 mayincrease the number of reference blocks in a range that is broader thanthe range of positions of blocks that neighbor current block 27.

With this, even when the capability of encoder 100 is low, encoder 100can perform processing of an amount processable by encoder 100 andwithin the range of memory capacity of encoder 100.

Moreover, for example, when the size of current picture 25 is a firstsize that is larger than a third reference, the predetermined intervalof the blocks (i) positioned in a range that is broader than the rangeof positions of blocks that neighbor current block 27 and (ii) spacedapart by the predetermined interval may be a third interval, and whenthe size of current picture 25 is a second size that is smaller than thethird reference, the predetermined interval may be a fourth intervalthat is narrower than the third interval. In other words, when the sizeof current picture 25 is larger than a reference, encoder 100 may widenthe predetermined interval of blocks (i) positioned in a range that isbroader than the range of positions of blocks that neighbor currentblock 27 and (ii) spaced apart by the predetermined interval. Moreover,when the size of current picture 25 is smaller than a reference, encoder100 may narrow the predetermined interval of blocks (i) positioned in arange that is broader than the range of positions of blocks thatneighbor current block 27 and (ii) spaced apart by the predeterminedinterval.

Moreover, for example, when the size of current picture 25 is a thirdsize that is larger than a fourth reference, the number of referenceblocks in predetermined positions to be referenced for motion vectorpredictor list generation in a range that is broader than the range ofpositions of blocks neighboring current block 27 may be a third number,and when the size of current picture 25 is a fourth size that is smallerthan the fourth reference, the number of reference blocks inpredetermined positions to be referenced for motion vector predictorlist generation in a range that is broader than the range of positionsof blocks neighboring current block 27 may be a fourth number that isless than the third number. In other words, when the size of currentpicture 25 is larger than a reference, encoder 100 may increase thenumber of reference blocks in a range that is broader than the range ofpositions of blocks that neighbor current block 27. Moreover, when thesize of current picture 25 is smaller than a reference, encoder 100 mayreduce the number of reference blocks in a range that is broader thanthe range of positions of blocks that neighbor current block 27.

With this, when the size of current picture 25 is large, encoder 100 canreference a motion vector from a block positioned in a range that isbroader than when the size of current picture 25 is small. Accordingly,compared to when encoder 100 does not perform the above method, encoder100 can obtain motion vector predictors more appropriately, and canimprove coding efficiency.

Moreover, encoder 100 may store information on motion vectors assignedto reference blocks in memory.

Moreover, circuitry 150 may store information on motion vectors in unitsof reference blocks in memory 152, and when current block 27 is a blockincluding a reference block at a position defined by the regularinterval, may store information on motion vectors derived from currentblock 27 in memory 152.

FIG. 19 is a block diagram illustrating an implementation example of adecoder according to Embodiment 1. Decoder 200 includes circuitry 250and memory 252. For example, the plurality of elements included indecoder 200 illustrated in FIG. 10 are implemented as circuitry 250 andmemory 252 illustrated in FIG. 19 .

Circuitry 250 is electronic circuitry that is capable of accessingmemory 252, and performs information processing. For example, circuitry250 is dedicated or generic electronic circuitry that decodes a videousing memory 252. Circuitry 250 may be a processor such as a CPU.Moreover, circuitry 250 may be an aggregate of a plurality of electroniccircuits.

Moreover, for example, circuitry 250 may perform the roles of aplurality of elements from among the plurality of elements included indecoder 200 illustrated in FIG. 10 , excluding elements for storinginformation. In other words, circuitry 250 may performed theabove-described operations as the operations performed by thoseelements.

Memory 252 is dedicated or generic memory that stores information forcircuitry 250 to decode a video. Memory 252 may be electronic circuitry,may be coupled to circuitry 250, and may be included in circuitry 250.

Moreover, memory 252 may be an aggregate of a plurality of electroniccircuits, and may be configured of a plurality of sub-memories.Moreover, memory 252 may be, for example, a magnetic disk or an opticaldisk, and may be realized as storage or a recording medium, for example.Moreover, memory 252 may be nonvolatile memory, and may be volatilememory.

For example, memory 252 may perform the roles of, from among theplurality of elements included in decoder 200 illustrated in FIG. 10 ,those for storing information.

Moreover, memory 252 may store a decoded video, and may store a sequenceof bits corresponding to a decoded video. Moreover, memory 252 may storea program for circuitry 250 to decode a video.

Note that not all of the plurality of elements illustrated in FIG. 10need to be implemented in decoder 200, and not all of theabove-described processes need to be performed. Some of the plurality ofelements illustrated in FIG. 10 may be included in some other device,and some of the above-described processes may be executed by some otherdevice. Then, due to some of the plurality of elements illustrated inFIG. 10 being implemented in decoder 200 and some of the above-describedprocesses being performed by decoder 200, information related to videodecoding can be appropriately configured.

FIG. 20 is a flow chart illustrating an example of operations performedby a decoder according to Embodiment 1. For example, decoder 200illustrated in FIG. 19 performs the processes illustrated in FIG. 20upon initializing probability parameters for entropy decoding.Specifically, circuitry 250 performs the following operations usingmemory 252.

First, decoder 200 generates a motion vector predictor list byregistering spatially neighboring motion vector predictors and spatiallybroad motion vector predictors (step S4001).

Next, decoder 200 selects one motion vector predictor from the motionvector predictor list (step S4002).

Decoder 200 then performs motion compensation on current block 27 usinga motion vector derived from the motion vector predictor (step S4003).Here, in the decoder 200, information on motion vectors to be referencedin prediction mode may be managed in association with reference blocksof a specific size, and the plurality of predetermined positions may bepositions of, from among the reference blocks, reference blocks atpositions defined by a regular interval using the top-left of thecurrent picture as a reference point.

Moreover, the processes illustrated in S4001 through S4003 and performedby decoder 200 may be performed in merge mode.

Moreover, decoder 200 may define blocks (i) positioned in a range thatis broader than the range of positions of blocks that neighbor currentblock 27 and (ii) spaced apart by a predetermined interval as referenceblocks having a specific size. Moreover, information on motion vectorsto be referenced by decoder 200 may be managed in association with thereference blocks.

Moreover, decoder 200 may be capable of adaptively switching, based onthe capability of decoder 200 or the size, etc., of current picture 25,the range of blocks positioned in a range that is broader than the rangeof positions of blocks that neighbor current block 27.

Moreover, decoder 200 may write, into the slice, picture, or sequenceheader, information specifying the interval of the blocks (i) positionedin a range that is broader than the range of positions of blocks thatneighbor current block 27 and (ii) spaced apart by a predeterminedinterval, or the range of positions of the blocks.

For example, when the capability of decoder 200 is a first capabilitythat is lower than a first reference, the predetermined interval of theblocks (i) positioned in a range that is broader than the range ofpositions of blocks that neighbor current block 27 and (ii) spaced apartby a predetermined interval may be a first interval, and when thecapability of decoder 200 is a second capability that is higher than thefirst reference, the predetermined interval may be a second intervalthat is narrower than the first interval. In other words, when thecapability of decoder 200 is lower than a reference, decoder 200 maynarrow the predetermined interval of blocks (i) positioned in a rangethat is broader than the range of positions of blocks that neighborcurrent block 27 and (ii) spaced apart by a predetermined interval.Moreover, when the capability of decoder 200 is higher than a reference,decoder 200 may widen the predetermined interval of blocks (i)positioned in a range that is broader than the range of positions ofblocks that neighbor current block 27 and (ii) spaced apart by apredetermined interval.

Moreover, for example, when the capability of decoder 200 is a thirdcapability that is lower than the second reference, the number ofreference blocks in predetermined positions to be referenced for motionvector predictor list generation in a range that is broader than therange of positions of blocks neighboring current block 27 may be a firstnumber, and when the capability of decoder 200 is a fourth capabilitythat is higher than the second reference, the number of reference blocksin predetermined positions to be referenced for motion vector predictorlist generation in a range that is broader than the range of positionsof blocks neighboring current block 27 may be a second number that isgreater than the first number. In other words, when the capability ofdecoder 200 is lower than a reference, decoder 200 may reduce the numberof reference blocks in a range that is broader than the range ofpositions of blocks that neighbor current block 27. Moreover, when thecapability of decoder 200 is higher than a reference, decoder 200 mayincrease the number of reference blocks in a range that is broader thanthe range of positions of blocks that neighbor current block 27.

With this, even when the capability of decoder 200 is low, decoder 200can perform processing of an amount processable by decoder 200 andwithin the range of memory capacity of decoder 200.

Moreover, for example, when the size of current picture 25 is a firstsize that is larger than a third reference, the predetermined intervalof the blocks (i) positioned in a range that is broader than the rangeof positions of blocks that neighbor current block 27 and (ii) spacedapart by the predetermined interval may be a third interval, and whenthe size of current picture 25 is a second size that is smaller than thethird reference, the predetermined interval may be a fourth intervalthat is narrower than the third interval. In other words, when the sizeof current picture 25 is larger than a reference, decoder 200 may widenthe predetermined interval of blocks (i) positioned in a range that isbroader than the range of positions of blocks that neighbor currentblock 27 and (ii) spaced apart by the predetermined interval. Moreover,when the size of current picture 25 is smaller than a reference, decoder200 may narrow the predetermined interval of blocks (i) positioned in arange that is broader than the range of positions of blocks thatneighbor current block 27 and (ii) spaced apart by the predeterminedinterval.

Moreover, for example, when the size of current picture 25 is a thirdsize that is larger than a fourth reference, the number of referenceblocks in predetermined positions to be referenced for motion vectorpredictor list generation in a range that is broader than the range ofpositions of blocks neighboring current block 27 may be a third number,and when the size of current picture 25 is a fourth size that is smallerthan the fourth reference, the number of reference blocks inpredetermined positions to be referenced for motion vector predictorlist generation in a range that is broader than the range of positionsof blocks neighboring current block 27 may be a fourth number that isless than the third number. In other words, when the size of currentpicture 25 is larger than a reference, decoder 200 may increase thenumber of reference blocks in a range that is broader than the range ofpositions of blocks that neighbor current block 27. Moreover, when thesize of current picture 25 is smaller than a reference, decoder 200 mayreduce the number of reference blocks in a range that is broader thanthe range of positions of blocks that neighbor current block 27.

With this, when the size of current picture 25 is large, decoder 200 canreference a motion vector from a block positioned in a range that isbroader than when the size of current picture 25 is small. Accordingly,compared to when decoder 200 does not perform the above method, decoder200 can obtain motion vector predictors more appropriately, and canimprove coding efficiency.

Moreover, decoder 200 may store information on motion vectors assignedto reference blocks in memory.

Moreover, circuitry 150 may store information on motion vectors assignedto reference blocks in memory 152, and when current block 27 is a blockincluding a reference block at a position defined by the regularinterval, may store information on motion vectors derived from currentblock 27 in memory 152.

[Supplemental Information]

Encoder 100 and decoder 200 according to this embodiment may be used asan image encoder and an image decoder, respectively, and may be used asa video encoder and a video decoder, respectively.

Note that in the above embodiment, each element may be configured in theform of dedicated hardware, or may be realized by executing a softwareprogram suitable for the elements. Each element may be realized by aprogram executing unit, such as a CPU or a processor, reading andexecuting the software program recorded on a recording medium such as ahard disk or semiconductor memory.

Specifically, encoder 100 and decoder 200 may include processingcircuitry and storage which is electrically coupled to the processingcircuitry and accessible from the processing circuitry. For example, theprocessing circuitry corresponds to circuitry 150 or 250, and thestorage corresponds to memory 152 or 252.

The processing circuitry includes at least one of dedicated hardware anda program executing unit, and executes processes using the storage. Inaddition, when the processing circuitry includes the program executingunit, the storage stores a software program that is executed by theprogram executing unit.

Here, the software for realizing, for example, encoder 100 or decoder200 according to this embodiment is a program as described below.

The program may cause a computer to execute an encoding method thatencodes a video and includes generating a motion vector predictor listby registering motion vector predictors obtained by referencing aplurality of encoded blocks, selects one motion vector predictor fromthe motion vector predictor list, and implements a prediction mode thatperforms motion compensation using a motion vector derived from the onemotion vector predictor. The motion vector predictor list may include aspatially neighboring motion vector predictor obtained from a blockspatially neighboring a current block, and a spatially broad motionvector predictor obtained from a block positioned at any of a pluralityof predetermined positions in a second range that is broader than afirst range that spatially neighbors the current block. The plurality ofpredetermined positions may be defined by a regular interval using atop-left of a current picture as a reference point.

The program may cause a computer to execute a decoding method thatdecodes a video and includes generating a motion vector predictor listby registering motion vector predictors obtained by referencing aplurality of decoded blocks, selects one motion vector predictor fromthe motion vector predictor list, and implements a prediction mode thatperforms motion compensation using a motion vector derived from the onemotion vector predictor. The motion vector predictor list may include aspatially neighboring motion vector predictor obtained from a blockspatially neighboring a current block, and a spatially broad motionvector predictor obtained from a block positioned at any of a pluralityof predetermined positions in a second range that is broader than afirst range that spatially neighbors the current block. The plurality ofpredetermined positions may be defined by a regular interval using atop-left of a current picture as a reference point.

Moreover, each element may be implemented as circuitry, as describedabove. Such circuitry may include a single comprehensive circuit or aplurality of circuits, one for each element. Moreover, each element maybe implemented as a general purpose processor, and may be implemented asa dedicated processor.

Processes executed by specific elements may be executed by otherelements. Moreover, the order of execution of the process may bechanged, and a plurality of processes may be executed in parallel.Moreover, the encoder/decoder may include both encoder 100 and decoder200.

Moreover, the ordinal numbers such as “first” and “second” used in thedescription may be changed where appropriate. New ordinal numbers may beapplied to, for example, the elements, and the ordinal numbers may beremoved from, for example, the elements.

Hereinbefore, an aspect of encoder 100 and decoder 200 has beendescribed based on an embodiment, but aspects of encoder 100 and decoder200 are not limited to this embodiment. Aspects of encoder 100 anddecoder 200 may also encompass various modifications that may beconceived by those skilled in the art to the embodiments, andembodiments achieved by combining elements in different embodiments,without departing from the scope of the present disclosure.

The aspect may be implemented in combination with one or more of theother aspects according to the present disclosure. In addition, aportion of the processes in the flowcharts, a portion of the elementsincluded in the apparatuses, and a portion of the syntax described inthis aspect may be implemented in combination with other aspects.

Embodiment 2

As described in each of the above embodiments, each functional block cantypically be realized as an MPU and memory, for example. Moreover,processes performed by each of the functional blocks are typicallyrealized by a program execution unit, such as a processor, reading andexecuting software (a program) recorded on a recording medium such asROM. The software may be distributed via, for example, downloading, andmay be recorded on a recording medium such as semiconductor memory anddistributed. Note that each functional block can, of course, also berealized as hardware (dedicated circuit).

Moreover, the processing described in each of the embodiments may berealized via integrated processing using a single apparatus (system),and, alternatively, may be realized via decentralized processing using aplurality of apparatuses. Moreover, the processor that executes theabove-described program may be a single processor or a plurality ofprocessors. In other words, integrated processing may be performed, and,alternatively, decentralized processing may be performed.

Embodiments of the present disclosure are not limited to the aboveexemplary embodiments; various modifications may be made to theexemplary embodiments, the results of which are also included within thescope of the embodiments of the present disclosure.

Next, application examples of the moving picture encoding method (imageencoding method) and the moving picture decoding method (image decodingmethod) described in each of the above embodiments and a system thatemploys the same will be described. The system is characterized asincluding an image encoder that employs the image encoding method, animage decoder that employs the image decoding method, and an imageencoder/decoder that includes both the image encoder and the imagedecoder. Other configurations included in the system may be modified ona case-by-case basis.

Usage Examples

FIG. 21 illustrates an overall configuration of content providing systemex100 for implementing a content distribution service. The area in whichthe communication service is provided is divided into cells of desiredsizes, and base stations ex106, ex107, ex108, ex109, and ex110, whichare fixed wireless stations, are located in respective cells.

In content providing system ex100, devices including computer ex111,gaming device ex112, camera ex113, home appliance ex114, and smartphoneex115 are connected to internet ex101 via internet service providerex102 or communications network ex104 and base stations ex106 throughex110. Content providing system ex100 may combine and connect anycombination of the above elements. The devices may be directly orindirectly connected together via a telephone network or near fieldcommunication rather than via base stations ex106 through ex110, whichare fixed wireless stations. Moreover, streaming server ex103 isconnected to devices including computer ex111, gaming device ex112,camera ex113, home appliance ex114, and smartphone ex115 via, forexample, internet ex101. Streaming server ex103 is also connected to,for example, a terminal in a hotspot in airplane ex117 via satelliteex116.

Note that instead of base stations ex106 through ex110, wireless accesspoints or hotspots may be used. Streaming server ex103 may be connectedto communications network ex104 directly instead of via internet ex101or internet service provider ex102, and may be connected to airplaneex117 directly instead of via satellite ex116.

Camera ex113 is a device capable of capturing still images and video,such as a digital camera. Smartphone ex115 is a smartphone device,cellular phone, or personal handyphone system (PHS) phone that canoperate under the mobile communications system standards of the typical2G, 3G, 3.9G, and 4G systems, as well as the next-generation 5G system.

Home appliance ex118 is, for example, a refrigerator or a deviceincluded in a home fuel cell cogeneration system.

In content providing system ex100, a terminal including an image and/orvideo capturing function is capable of, for example, live streaming byconnecting to streaming server ex103 via, for example, base stationex106. When live streaming, a terminal (e.g., computer ex111, gamingdevice ex112, camera ex113, home appliance ex114, smartphone ex115, orairplane ex117) performs the encoding processing described in the aboveembodiments on still-image or video content captured by a user via theterminal, multiplexes video data obtained via the encoding and audiodata obtained by encoding audio corresponding to the video, andtransmits the obtained data to streaming server ex103. In other words,the terminal functions as the image encoder according to one aspect ofthe present disclosure.

Streaming server ex103 streams transmitted content data to clients thatrequest the stream. Client examples include computer ex111, gamingdevice ex112, camera ex113, home appliance ex114, smartphone ex115, andterminals inside airplane ex117, which are capable of decoding theabove-described encoded data. Devices that receive the streamed datadecode and reproduce the received data. In other words, the devices eachfunction as the image decoder according to one aspect of the presentdisclosure.

[Decentralized Processing]

Streaming server ex103 may be realized as a plurality of servers orcomputers between which tasks such as the processing, recording, andstreaming of data are divided. For example, streaming server ex103 maybe realized as a content delivery network (CDN) that streams content viaa network connecting multiple edge servers located throughout the world.In a CDN, an edge server physically near the client is dynamicallyassigned to the client. Content is cached and streamed to the edgeserver to reduce load times. In the event of, for example, some kind ofan error or a change in connectivity due to, for example, a spike intraffic, it is possible to stream data stably at high speeds since it ispossible to avoid affected parts of the network by, for example,dividing the processing between a plurality of edge servers or switchingthe streaming duties to a different edge server, and continuingstreaming.

Decentralization is not limited to just the division of processing forstreaming; the encoding of the captured data may be divided between andperformed by the terminals, on the server side, or both. In one example,in typical encoding, the processing is performed in two loops. The firstloop is for detecting how complicated the image is on a frame-by-frameor scene-by-scene basis, or detecting the encoding load. The second loopis for processing that maintains image quality and improves encodingefficiency. For example, it is possible to reduce the processing load ofthe terminals and improve the quality and encoding efficiency of thecontent by having the terminals perform the first loop of the encodingand having the server side that received the content perform the secondloop of the encoding. In such a case, upon receipt of a decodingrequest, it is possible for the encoded data resulting from the firstloop performed by one terminal to be received and reproduced on anotherterminal in approximately real time. This makes it possible to realizesmooth, real-time streaming.

In another example, camera ex113 or the like extracts a feature amountfrom an image, compresses data related to the feature amount asmetadata, and transmits the compressed metadata to a server. Forexample, the server determines the significance of an object based onthe feature amount and changes the quantization accuracy accordingly toperform compression suitable for the meaning of the image. Featureamount data is particularly effective in improving the precision andefficiency of motion vector prediction during the second compressionpass performed by the server. Moreover, encoding that has a relativelylow processing load, such as variable length coding (VLC), may behandled by the terminal, and encoding that has a relatively highprocessing load, such as context-adaptive binary arithmetic coding(CABAC), may be handled by the server.

In yet another example, there are instances in which a plurality ofvideos of approximately the same scene are captured by a plurality ofterminals in, for example, a stadium, shopping mall, or factory. In sucha case, for example, the encoding may be decentralized by dividingprocessing tasks between the plurality of terminals that captured thevideos and, if necessary, other terminals that did not capture thevideos and the server, on a per-unit basis. The units may be, forexample, groups of pictures (GOP), pictures, or tiles resulting fromdividing a picture. This makes it possible to reduce load times andachieve streaming that is closer to real-time.

Moreover, since the videos are of approximately the same scene,management and/or instruction may be carried out by the server so thatthe videos captured by the terminals can be cross-referenced. Moreover,the server may receive encoded data from the terminals, change referencerelationship between items of data or correct or replace picturesthemselves, and then perform the encoding. This makes it possible togenerate a stream with increased quality and efficiency for theindividual items of data.

Moreover, the server may stream video data after performing transcodingto convert the encoding format of the video data. For example, theserver may convert the encoding format from MPEG to VP, and may convertH.264 to H.265.

In this way, encoding can be performed by a terminal or one or moreservers. Accordingly, although the device that performs the encoding isreferred to as a “server” or “terminal” in the following description,some or all of the processes performed by the server may be performed bythe terminal, and likewise some or all of the processes performed by theterminal may be performed by the server. This also applies to decodingprocesses.

[3D, Multi-Angle]

In recent years, usage of images or videos combined from images orvideos of different scenes concurrently captured or the same scenecaptured from different angles by a plurality of terminals such ascamera ex113 and/or smartphone ex115 has increased. Videos captured bythe terminals are combined based on, for example, theseparately-obtained relative positional relationship between theterminals, or regions in a video having matching feature points.

In addition to the encoding of two-dimensional moving pictures, theserver may encode a still image based on scene analysis of a movingpicture either automatically or at a point in time specified by theuser, and transmit the encoded still image to a reception terminal.Furthermore, when the server can obtain the relative positionalrelationship between the video capturing terminals, in addition totwo-dimensional moving pictures, the server can generatethree-dimensional geometry of a scene based on video of the same scenecaptured from different angles. Note that the server may separatelyencode three-dimensional data generated from, for example, a pointcloud, and may, based on a result of recognizing or tracking a person orobject using three-dimensional data, select or reconstruct and generatea video to be transmitted to a reception terminal from videos capturedby a plurality of terminals.

This allows the user to enjoy a scene by freely selecting videoscorresponding to the video capturing terminals, and allows the user toenjoy the content obtained by extracting, from three-dimensional datareconstructed from a plurality of images or videos, a video from aselected viewpoint. Furthermore, similar to with video, sound may berecorded from relatively different angles, and the server may multiplex,with the video, audio from a specific angle or space in accordance withthe video, and transmit the result.

In recent years, content that is a composite of the real world and avirtual world, such as virtual reality (VR) and augmented reality (AR)content, has also become popular. In the case of VR images, the servermay create images from the viewpoints of both the left and right eyesand perform encoding that tolerates reference between the two viewpointimages, such as multi-view coding (MVC), and, alternatively, may encodethe images as separate streams without referencing. When the images aredecoded as separate streams, the streams may be synchronized whenreproduced so as to recreate a virtual three-dimensional space inaccordance with the viewpoint of the user.

In the case of AR images, the server superimposes virtual objectinformation existing in a virtual space onto camera informationrepresenting a real-world space, based on a three-dimensional positionor movement from the perspective of the user. The decoder may obtain orstore virtual object information and three-dimensional data, generatetwo-dimensional images based on movement from the perspective of theuser, and then generate superimposed data by seamlessly connecting theimages. Alternatively, the decoder may transmit, to the server, motionfrom the perspective of the user in addition to a request for virtualobject information, and the server may generate superimposed data basedon three-dimensional data stored in the server in accordance with thereceived motion, and encode and stream the generated superimposed datato the decoder. Note that superimposed data includes, in addition to RGBvalues, an a value indicating transparency, and the server sets the avalue for sections other than the object generated fromthree-dimensional data to, for example, 0, and may perform the encodingwhile those sections are transparent. Alternatively, the server may setthe background to a predetermined RGB value, such as a chroma key, andgenerate data in which areas other than the object are set as thebackground.

Decoding of similarly streamed data may be performed by the client(i.e., the terminals), on the server side, or divided therebetween. Inone example, one terminal may transmit a reception request to a server,the requested content may be received and decoded by another terminal,and a decoded signal may be transmitted to a device having a display. Itis possible to reproduce high image quality data by decentralizingprocessing and appropriately selecting content regardless of theprocessing ability of the communications terminal itself. In yet anotherexample, while a TV, for example, is receiving image data that is largein size, a region of a picture, such as a tile obtained by dividing thepicture, may be decoded and displayed on a personal terminal orterminals of a viewer or viewers of the TV. This makes it possible forthe viewers to share a big-picture view as well as for each viewer tocheck his or her assigned area or inspect a region in further detail upclose.

In the future, both indoors and outdoors, in situations in which aplurality of wireless connections are possible over near, mid, and fardistances, it is expected to be able to seamlessly receive content evenwhen switching to data appropriate for the current connection, using astreaming system standard such as MPEG-DASH. With this, the user canswitch between data in real time while freely selecting a decoder ordisplay apparatus including not only his or her own terminal, but also,for example, displays disposed indoors or outdoors. Moreover, based on,for example, information on the position of the user, decoding can beperformed while switching which terminal handles decoding and whichterminal handles the displaying of content. This makes it possible to,while in route to a destination, display, on the wall of a nearbybuilding in which a device capable of displaying content is embedded oron part of the ground, map information while on the move. Moreover, itis also possible to switch the bit rate of the received data based onthe accessibility to the encoded data on a network, such as when encodeddata is cached on a server quickly accessible from the receptionterminal or when encoded data is copied to an edge server in a contentdelivery service.

[Scalable Encoding]

The switching of content will be described with reference to a scalablestream, illustrated in FIG. 22 , that is compression coded viaimplementation of the moving picture encoding method described in theabove embodiments. The server may have a configuration in which contentis switched while making use of the temporal and/or spatial scalabilityof a stream, which is achieved by division into and encoding of layers,as illustrated in FIG. 22 . Note that there may be a plurality ofindividual streams that are of the same content but different quality.In other words, by determining which layer to decode up to based oninternal factors, such as the processing ability on the decoder side,and external factors, such as communication bandwidth, the decoder sidecan freely switch between low resolution content and high resolutioncontent while decoding. For example, in a case in which the user wantsto continue watching, at home on a device such as a TV connected to theinternet, a video that he or she had been previously watching onsmartphone ex115 while on the move, the device can simply decode thesame stream up to a different layer, which reduces server side load.

Furthermore, in addition to the configuration described above in whichscalability is achieved as a result of the pictures being encoded perlayer and the enhancement layer is above the base layer, the enhancementlayer may include metadata based on, for example, statisticalinformation on the image, and the decoder side may generate high imagequality content by performing super-resolution imaging on a picture inthe base layer based on the metadata. Super-resolution imaging may beimproving the SN ratio while maintaining resolution and/or increasingresolution. Metadata includes information for identifying a linear or anon-linear filter coefficient used in super-resolution processing, orinformation identifying a parameter value in filter processing, machinelearning, or least squares method used in super-resolution processing.

Alternatively, a configuration in which a picture is divided into, forexample, tiles in accordance with the meaning of, for example, an objectin the image, and on the decoder side, only a partial region is decodedby selecting a tile to decode, is also acceptable. Moreover, by storingan attribute about the object (person, car, ball, etc.) and a positionof the object in the video (coordinates in identical images) asmetadata, the decoder side can identify the position of a desired objectbased on the metadata and determine which tile or tiles include thatobject. For example, as illustrated in FIG. 23 , metadata is storedusing a data storage structure different from pixel data such as an SEImessage in HEVC. This metadata indicates, for example, the position,size, or color of the main object.

Moreover, metadata may be stored in units of a plurality of pictures,such as stream, sequence, or random access units. With this, the decoderside can obtain, for example, the time at which a specific personappears in the video, and by fitting that with picture unit information,can identify a picture in which the object is present and the positionof the object in the picture.

[Web Page Optimization]

FIG. 24 illustrates an example of a display screen of a web page on, forexample, computer ex111. FIG. 25 illustrates an example of a displayscreen of a web page on, for example, smartphone ex115. As illustratedin FIG. 24 and FIG. 25 , a web page may include a plurality of imagelinks which are links to image content, and the appearance of the webpage differs depending on the device used to view the web page. When aplurality of image links are viewable on the screen, until the userexplicitly selects an image link, or until the image link is in theapproximate center of the screen or the entire image link fits in thescreen, the display apparatus (decoder) displays, as the image links,still images included in the content or I pictures, displays video suchas an animated gif using a plurality of still images or I pictures, forexample, or receives only the base layer and decodes and displays thevideo.

When an image link is selected by the user, the display apparatusdecodes giving the highest priority to the base layer. Note that ifthere is information in the HTML code of the web page indicating thatthe content is scalable, the display apparatus may decode up to theenhancement layer. Moreover, in order to guarantee real timereproduction, before a selection is made or when the bandwidth isseverely limited, the display apparatus can reduce delay between thepoint in time at which the leading picture is decoded and the point intime at which the decoded picture is displayed (that is, the delaybetween the start of the decoding of the content to the displaying ofthe content) by decoding and displaying only forward reference pictures(I picture, P picture, forward reference B picture). Moreover, thedisplay apparatus may purposely ignore the reference relationshipbetween pictures and coarsely decode all B and P pictures as forwardreference pictures, and then perform normal decoding as the number ofpictures received over time increases.

[Autonomous Driving]

When transmitting and receiving still image or video data such two- orthree-dimensional map information for autonomous driving or assisteddriving of an automobile, the reception terminal may receive, inaddition to image data belonging to one or more layers, information on,for example, the weather or road construction as metadata, and associatethe metadata with the image data upon decoding. Note that metadata maybe assigned per layer and, alternatively, may simply be multiplexed withthe image data.

In such a case, since the automobile, drone, airplane, etc., includingthe reception terminal is mobile, the reception terminal can seamlesslyreceive and decode while switching between base stations among basestations ex106 through ex110 by transmitting information indicating theposition of the reception terminal upon reception request. Moreover, inaccordance with the selection made by the user, the situation of theuser, or the bandwidth of the connection, the reception terminal candynamically select to what extent the metadata is received or to whatextent the map information, for example, is updated.

With this, in content providing system ex100, the client can receive,decode, and reproduce, in real time, encoded information transmitted bythe user.

[Streaming of Individual Content]

In content providing system ex100, in addition to high image quality,long content distributed by a video distribution entity, unicast ormulticast streaming of low image quality, short content from anindividual is also possible. Moreover, such content from individuals islikely to further increase in popularity. The server may first performediting processing on the content before the encoding processing inorder to refine the individual content. This may be achieved with, forexample, the following configuration.

In real-time while capturing video or image content or after the contenthas been captured and accumulated, the server performs recognitionprocessing based on the raw or encoded data, such as capture errorprocessing, scene search processing, meaning analysis, and/or objectdetection processing. Then, based on the result of the recognitionprocessing, the server—either when prompted or automatically—edits thecontent, examples of which include: correction such as focus and/ormotion blur correction; removing low-priority scenes such as scenes thatare low in brightness compared to other pictures or out of focus; objectedge adjustment; and color tone adjustment. The server encodes theedited data based on the result of the editing. It is known thatexcessively long videos tend to receive fewer views. Accordingly, inorder to keep the content within a specific length that scales with thelength of the original video, the server may, in addition to thelow-priority scenes described above, automatically clip out scenes withlow movement based on an image processing result. Alternatively, theserver may generate and encode a video digest based on a result of ananalysis of the meaning of a scene.

Note that there are instances in which individual content may includecontent that infringes a copyright, moral right, portrait rights, etc.Such an instance may lead to an unfavorable situation for the creator,such as when content is shared beyond the scope intended by the creator.Accordingly, before encoding, the server may, for example, edit imagesso as to blur faces of people in the periphery of the screen or blur theinside of a house, for example. Moreover, the server may be configuredto recognize the faces of people other than a registered person inimages to be encoded, and when such faces appear in an image, forexample, apply a mosaic filter to the face of the person. Alternatively,as pre- or post-processing for encoding, the user may specify, forcopyright reasons, a region of an image including a person or a regionof the background be processed, and the server may process the specifiedregion by, for example, replacing the region with a different image orblurring the region. If the region includes a person, the person may betracked in the moving picture, and the head region may be replaced withanother image as the person moves.

Moreover, since there is a demand for real-time viewing of contentproduced by individuals, which tends to be small in data size, thedecoder first receives the base layer as the highest priority andperforms decoding and reproduction, although this may differ dependingon bandwidth. When the content is reproduced two or more times, such aswhen the decoder receives the enhancement layer during decoding andreproduction of the base layer and loops the reproduction, the decodermay reproduce a high image quality video including the enhancementlayer. If the stream is encoded using such scalable encoding, the videomay be low quality when in an unselected state or at the start of thevideo, but it can offer an experience in which the image quality of thestream progressively increases in an intelligent manner. This is notlimited to just scalable encoding; the same experience can be offered byconfiguring a single stream from a low quality stream reproduced for thefirst time and a second stream encoded using the first stream as areference.

Other Usage Examples

The encoding and decoding may be performed by LSI ex500, which istypically included in each terminal. LSI ex500 may be configured of asingle chip or a plurality of chips. Software for encoding and decodingmoving pictures may be integrated into some type of a recording medium(such as a CD-ROM, a flexible disk, or a hard disk) that is readable by,for example, computer ex111, and the encoding and decoding may beperformed using the software. Furthermore, when smartphone ex115 isequipped with a camera, the video data obtained by the camera may betransmitted. In this case, the video data is coded by LSI ex500 includedin smartphone ex115.

Note that LSI ex500 may be configured to download and activate anapplication. In such a case, the terminal first determines whether it iscompatible with the scheme used to encode the content or whether it iscapable of executing a specific service. When the terminal is notcompatible with the encoding scheme of the content or when the terminalis not capable of executing a specific service, the terminal firstdownloads a codec or application software then obtains and reproducesthe content.

Aside from the example of content providing system ex100 that usesinternet ex101, at least the moving picture encoder (image encoder) orthe moving picture decoder (image decoder) described in the aboveembodiments may be implemented in a digital broadcasting system. Thesame encoding processing and decoding processing may be applied totransmit and receive broadcast radio waves superimposed with multiplexedaudio and video data using, for example, a satellite, even though thisis geared toward multicast whereas unicast is easier with contentproviding system ex100.

[Hardware Configuration]

FIG. 26 illustrates smartphone ex115. FIG. 27 illustrates aconfiguration example of smartphone ex115. Smartphone ex115 includesantenna ex450 for transmitting and receiving radio waves to and frombase station ex110, camera ex465 capable of capturing video and stillimages, and display ex458 that displays decoded data, such as videocaptured by camera ex465 and video received by antenna ex450. Smartphoneex115 further includes user interface ex466 such as a touch panel, audiooutput unit ex457 such as a speaker for outputting speech or otheraudio, audio input unit ex456 such as a microphone for audio input,memory ex467 capable of storing decoded data such as captured video orstill images, recorded audio, received video or still images, and mail,as well as decoded data, and slot ex464 which is an interface for SIMex468 for authorizing access to a network and various data. Note thatexternal memory may be used instead of memory ex467.

Moreover, main controller ex460 which comprehensively controls displayex458 and user interface ex466, power supply circuit ex461, userinterface input controller ex462, video signal processor ex455, camerainterface ex463, display controller ex459, modulator/demodulator ex452,multiplexer/demultiplexer ex453, audio signal processor ex454, slotex464, and memory ex467 are connected via bus ex470.

When the user turns the power button of power supply circuit ex461 on,smartphone ex115 is powered on into an operable state by each componentbeing supplied with power from a battery pack.

Smartphone ex115 performs processing for, for example, calling and datatransmission, based on control performed by main controller ex460, whichincludes a CPU, ROM, and RAM. When making calls, an audio signalrecorded by audio input unit ex456 is converted into a digital audiosignal by audio signal processor ex454, and this is applied with spreadspectrum processing by modulator/demodulator ex452 and digital-analogconversion and frequency conversion processing by transmitter/receiverex451, and then transmitted via antenna ex450. The received data isamplified, frequency converted, and analog-digital converted, inversespread spectrum processed by modulator/demodulator ex452, converted intoan analog audio signal by audio signal processor ex454, and then outputfrom audio output unit ex457. In data transmission mode, text,still-image, or video data is transmitted by main controller ex460 viauser interface input controller ex462 as a result of operation of, forexample, user interface ex466 of the main body, and similar transmissionand reception processing is performed. In data transmission mode, whensending a video, still image, or video and audio, video signal processorex455 compression encodes, via the moving picture encoding methoddescribed in the above embodiments, a video signal stored in memoryex467 or a video signal input from camera ex465, and transmits theencoded video data to multiplexer/demultiplexer ex453. Moreover, audiosignal processor ex454 encodes an audio signal recorded by audio inputunit ex456 while camera ex465 is capturing, for example, a video orstill image, and transmits the encoded audio data tomultiplexer/demultiplexer ex453. Multiplexer/demultiplexer ex453multiplexes the encoded video data and encoded audio data using apredetermined scheme, modulates and converts the data usingmodulator/demodulator (modulator/demodulator circuit) ex452 andtransmitter/receiver ex451, and transmits the result via antenna ex450.

When video appended in an email or a chat, or a video linked from a webpage, for example, is received, in order to decode the multiplexed datareceived via antenna ex450, multiplexer/demultiplexer ex453demultiplexes the multiplexed data to divide the multiplexed data into abitstream of video data and a bitstream of audio data, supplies theencoded video data to video signal processor ex455 via synchronous busex470, and supplies the encoded audio data to audio signal processorex454 via synchronous bus ex470. Video signal processor ex455 decodesthe video signal using a moving picture decoding method corresponding tothe moving picture encoding method described in the above embodiments,and video or a still image included in the linked moving picture file isdisplayed on display ex458 via display controller ex459. Moreover, audiosignal processor ex454 decodes the audio signal and outputs audio fromaudio output unit ex457. Note that since real-time streaming is becomingmore and more popular, there are instances in which reproduction of theaudio may be socially inappropriate depending on the user's environment.Accordingly, as an initial value, a configuration in which only videodata is reproduced, i.e., the audio signal is not reproduced, ispreferable. Audio may be synchronized and reproduced only when an input,such as when the user clicks video data, is received.

Although smartphone ex115 was used in the above example, threeimplementations are conceivable: a transceiver terminal including bothan encoder and a decoder; a transmitter terminal including only anencoder; and a receiver terminal including only a decoder. Further, inthe description of the digital broadcasting system, an example is givenin which multiplexed data obtained as a result of video data beingmultiplexed with, for example, audio data, is received or transmitted,but the multiplexed data may be video data multiplexed with data otherthan audio data, such as text data related to the video. Moreover, thevideo data itself rather than multiplexed data maybe received ortransmitted.

Although main controller ex460 including a CPU is described ascontrolling the encoding or decoding processes, terminals often includeGPUs. Accordingly, a configuration is acceptable in which a large areais processed at once by making use of the performance ability of the GPUvia memory shared by the CPU and GPU or memory including an address thatis managed so as to allow common usage by the CPU and GPU. This makes itpossible to shorten encoding time, maintain the real-time nature of thestream, and reduce delay. In particular, processing relating to motionestimation, deblocking filtering, sample adaptive offset (SAO), andtransformation/quantization can be effectively carried out by the GPUinstead of the CPU in units of, for example pictures, all at once.

INDUSTRIAL APPLICABILITY

The present disclosure is applicable to, for example, televisionreceivers, digital video recorders, car navigation systems, mobilephones, digital cameras, digital video cameras, video conferencesystems, and electron mirrors.

The invention claimed is:
 1. An encoder that encodes a video, theencoder comprising: circuitry; and memory, wherein, using the memory,the circuitry: generates a motion vector predictor list by registeringmotion vectors obtained by referencing a plurality of encoded blocks,selects one motion vector predictor from the motion vector predictorlist, and implements a prediction mode that performs motion compensationon a current block using a motion vector derived from the one motionvector predictor, the motion vector predictor list includes (i) a firstmotion vector predictor obtained from a block in a first range thatspatially neighbors the current block, and (ii) a second motion vectorpredictor obtained from a block positioned at any of a plurality ofpredetermined positions in a second range that is broader than the firstrange, information on motion vectors to be referenced in the predictionmode is managed in association with reference blocks of a specific size,and the plurality of predetermined positions are positions of referenceblocks in positions defined by a regular interval using a currentpicture including the current block as a reference.
 2. A decoder thatdecodes a video, the decoder comprising: circuitry; and memory, wherein,using the memory, the circuitry: generates a motion vector predictorlist by registering motion vectors obtained by referencing a pluralityof decoded blocks, selects one motion vector predictor from the motionvector predictor list, and implements a prediction mode that performsmotion compensation on a current block using a motion vector derivedfrom the one motion vector predictor, the motion vector predictor listincludes (i) a first motion vector predictor obtained from a block in afirst range that spatially neighbors the current block, and (ii) asecond motion vector predictor obtained from a block positioned at anyof a plurality of predetermined positions in a second range that isbroader than the first range, information on motion vectors to bereferenced in the prediction mode is managed in association withreference blocks of a specific size, and the plurality of predeterminedpositions are positions of reference blocks in positions defined by aregular interval using a current picture including the current block asa reference point.
 3. An encoding method of encoding a video, theencoding method comprising: generating a motion vector predictor list byregistering motion vectors obtained by referencing a plurality ofencoded blocks, selects one motion vector predictor from the motionvector predictor list, and implements a prediction mode that performsmotion compensation on a current block using a motion vector derivedfrom the one motion vector predictor, wherein the motion vectorpredictor list includes (i) a first motion vector predictor obtainedfrom a block in a first range that spatially neighbors the currentblock, and (ii) a second motion vector predictor obtained from a blockpositioned at any of a plurality of predetermined positions in a secondrange that is broader than the first range, and the plurality ofpredetermined positions are defined by a regular interval using acurrent picture including the current block as a reference point.
 4. Adecoding method of decoding a video, the decoding method comprising:generating a motion vector predictor list by registering motion vectorsobtained by referencing a plurality of decoded blocks, selects onemotion vector predictor from the motion vector predictor list, andimplements a prediction mode that performs motion compensation on acurrent block using a motion vector derived from the one motion vectorpredictor, wherein the motion vector predictor list includes (i) a firstmotion vector predictor obtained from a block in a first range thatspatially neighbors the current block, and (ii) a second motion vectorpredictor obtained from a block positioned at any of a plurality ofpredetermined positions in a second range that is broader than the firstrange, and the plurality of predetermined positions are defined by aregular interval using a current picture including the current block asa reference point.